NRI INSTITUTE OF TECHNOLOGY

Transcription

1 NRI INSTITUTE OF TECHNOLOGY (Approved by AICTE, New Delhi: Affiliated to JNTUK, Kakinada) POTHAVARAPPADU (V), (via) Nunna, Agiripalli (M), Krishna District, A.P. PIN: Ph: Website: nrigroupofcolleges.com ELECTRONIC DEVICES & CIRCUITS LAB MANUAL II B.TECH 1 ST SEMESTER ECE DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING R16 REGULATION, ACADEMIC YEAR:

2 NRI INSTITUTE OF TECHNOLOGY (Approved by AICTE, New Delhi: Affiliated to JNTUK, Kakinada) POTHAVARAPPADU (V), (via) Nunna, Agiripalli (M), Krishna District, A.P. PIN: Ph: Website: nrigroupofcolleges.com ELECTRONIC DEVICES & CIRCUITS LAB OBSERVATION BOOK II B.TECH 1 ST SEMESTER ECE DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING R16 REGULATION, ACADEMIC YEAR:

3 PART-I INDEX STUDENT NAME: REG NO: BRANCH/SEC : II/IV YEAR : S.No NAME OF THE COMPONENT/EQUIPMENT PAGE No. DATE SIG. OF STAFF REMARKS 1 Colour coding of Resistors 1 2 Variable Resistors 5 3 Colour coding of Capacitors 7 4 Switches 13 5 Relays 18 6 Bread Board 19 7 Diodes 20 8 Transistors - Bipolar junction transistor 23 9 SCR- Silicon Controlled Rectifier 27 9 Uni Junction Transistor Field Effect Transistor Soldering guide Multimeters Function Generators Cathode Ray Oscilloscope Regulated Power Supply Coils Inductor 55 Signature of Staff Member/Date

4 PART-II INDEX S.No NAME OF THE EXPERIMENT DATE PAGE No. SIGNATURE REMARKS 1 PN Junction Diode Characteristics Zener Diode Characteristics and Zener as a regulator Half Wave Rectifiers With & Without Filters Full Wave Rectifiers With & Without Filters Transistor Common Base Characteristics 36 6 Transistor Common Emitter Characteristics 44 7 Common Emitter Amplifier 52 8 Common Collector Amplifier 58 9 FET Characteristics UJT characteristics SCR characteristics Frequency measurement using Lissajous figures 85 No. of Experiments completed: Average marks awarded for day to day work: Signature of Staff Member/Date

5 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL COLOR CODING OF RESISTORS FUNCTION: Resistors restrict the flow of electric current. Example: Circuit symbol: Resistors may be connected either way round. They are not damaged by heat when soldering. Resistor values - the resistor color code Resistance is measured in ohms, the symbol for ohm is an omega. 1 is quite small so resistor values are often given in k and M. 1 k = M = 10,00,000. Resistor values are normally shown using color bands. Each color represents a number as shown in the table. Most resistors have 4 bands: The first band gives the first digit. The second band gives the second digit. The third band indicates the number of zeros. The fourth band indicates the tolerance (precision) of the resistor. Ex: This resistor has red (2), violet (7), yellow (4 zeros) and gold bands. So its value is 270,000 = 270 k. On circuit diagrams the is usually omitted and the value is written 270K. Small value resistors (less than 10 ohm) The Resistor Colour Code Colour Number Black 0 Brown 1 Red 2 Orange 3 Yellow 4 Green 5 Blue 6 Violet 7 Grey 8 White 9 The standard color code cannot show values of less than 10. To show these small values two special colors are used for the third band: gold which means 0.1 and silver which means The first and second bands represent the digits as normal. For example: red, violet, gold bands represent = 2.7 green, blue, silver bands represent = 0.56 Tolerance of resistors (fourth band of color code) The tolerance of a resistor is shown by the fourth band of the color code. Tolerance is the precision of the resistor and it is given as a percentage. Ex: 390 resistor with a tolerance of ±10% will have a value within 10% of 390, between = 351 and = 429 (39 is 10% of 390). PART I PAGE 1

6 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL A special colour code is used for the fourth band tolerance: silver ±10%, gold ±5%, red ±2%, brown ±1%. If no fourth band is shown the tolerance is ±20%. Tolerance may be ignored for almost all circuits because precise resistor values are rarely required. Resistor shorthand Resistor values are often written on circuit diagrams using a code system which avoids using a decimal point because it is easy to miss the small dot. Instead the letters R, K and M are used in place of the decimal point. To read the code: replace the letter with a decimal point, then multiply the value by 1000 if the letter was K, or if the letter was M. The letter R means multiply by 1. Example: 560R means 560 2K7 means 2.7 k = K means 39 k 1M0 means 1.0 M = 1000 k Real resistor values (the E6 and E12 series) Resistors are not available with every possible value, for example 22k and 47k are readily available, but 25k and 50k are not! Why is this? Imagine that you decided to make resistors every 10 giving 10, 20, 30, 40, 50 and so on. That seems fine, but what happens when you reach 1000? It would be pointless to make 1000, 1010, 1020, 1030 and so on because for these values 10 is a very small difference, too small to be noticeable in most circuits. In fact it would be difficult to make resistors sufficiently accurate. To produce a sensible range of resistor values you need to increase the size of the 'step' as the value increases. The standard resistor values are based on this idea and they form a series which follows the same pattern for every multiple of ten. The E6 series (6 values for each multiple of ten, for resistors with 20% tolerance)10, 15, 22, 33, 47, 68,... then it continues 100, 150, 220, 330, 470, 680, 1000 etc. Notice how the step size increases as the value increases. For this series the step (to the next value) is roughly half the value. The E12 series (12 values for each multiple of ten, for resistors with 10% tolerance)10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82,... then it continues 100, 120, 150 etc. Notice how this is the E6 series with an extra value in the gaps. The E12 series is the one most frequently used for resistors. It allows you to choose a value within 10% of the precise value you need. This is sufficiently accurate for almost all projects and it is sensible because most resistors are only accurate to ±10% (called their 'tolerance'). For example a resistor marked 390 could vary by ±10% 390 = ±39, so it could be any value between 351 and 429. PART I PAGE 2

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9 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL VARIABLE RESISTORS Construction Variable resistors consist of a resistance track with connections at both ends and a wiper which moves along the track as you turn the spindle. The track may be made from carbon, cermet (ceramic and metal mixture) or a coil of wire (for low resistances). The track is usually rotary but straight track versions, usually called sliders, are also available. Variable resistors are often called potentiometers in books and catalogues. They are specified by their maximum resistance, linear or logarithmic track, and their physical size. The standard spindle diameter is 6mm. The resistance and type of track are marked on the body: Standard Variable Resistor 4K7 LIN means 4.7 k linear track. 1M LOG means 1 M logarithmic track. Rheostat This is the simplest way of using a variable resistor. Two terminals are used: one connected to an end of the track, the other to the moveable wiper. Turning the spindle changes the resistance between the two terminals from zero up to the maximum Rheostat Symbol resistance. Rheostats are often used to vary current, for example to control the brightness of a lamp or the rate at which a capacitor charges. If the rheostat is mounted on a printed circuit board you may find that all three terminals are connected! However, one of them will be linked to the wiper terminal. This improves the mechanical strength of the mounting but it serves no function electrically. Potentiometer Variable resistors used as potentiometers have all three terminals connected. Potentiometer Symbol This arrangement is normally used to vary voltage, for example to set the switching point of a circuit with a sensor, or control the volume (loudness) in an amplifier circuit. If the terminals at the ends of the track are connected across the power supply then the wiper terminal will provide a voltage which can be varied from zero up to the maximum of the supply. PART I PAGE 5

10 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL Presets: These are miniature versions of the standard variable resistor. They are designed to be mounted directly onto the circuit board and adjusted only when the circuit is built. For example: to set the frequency of an alarm tone or the sensitivity of a lightsensitive circuit. A small screwdriver or similar tool is required to adjust presets. Preset Symbol Presets are much cheaper than standard variable resistors so they are sometimes used in projects where a standard variable resistor would normally be used. Multiturn presets are used where very precise adjustments must be made. The screw must be turned many times (10+) to move the slider from one end of the track to the other, giving very fine control. Preset (open style) Multi turn preset PART I PAGE 6

11 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL COLOUR CODING OF CAPACITORS Capacitors store electric charge. used with resistors in timing circuits because it takes time for a capacitor to fill with charge. used to smooth varying DC supplies by acting as a reservoir of charge. used in filter circuits because capacitors easily pass AC (changing) signals blocks DC (constant) signals. Capacitance: It is a measure of a capacitor's ability to store charge. A large capacitance means that more charge can be stored. Capacitance is measured in farads, symbol F. However 1F is very large, so prefixes are used to show the smaller values. Three prefixes (multipliers) are used, µ (micro), n (nano) and p (pico): o µ means 10-6 (millionth), so µF = 1F o n means 10-9 (thousand-millionth), so 1000nF = 1µF o p means (million-millionth), so 1000pF = 1nF Capacitors are split into two groups - polarised and unpolarised. Each group has its own circuit symbol. POLARISED CAPACITORS (LARGE VALUES, 1µF +) Circuit symbol: Electrolytic Capacitors: Electrolytic capacitors are polarized They must be connected the correct way round, at least one of their leads will be marked + or -. They are not damaged by heat when soldering. There are two designs of electrolytic capacitors; axial where the leads are attached to each end (220µF in picture) and radial where both leads are at the same end (10µF in picture). Radial capacitors tend to be a little smaller and they stand upright on the circuit board. PART I PAGE 7

12 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL It is easy to find the value of electrolytic capacitors because they are clearly printed with their capacitance and voltage rating. The voltage rating can be quite low (6V for example) and it should always be checked when selecting an electrolytic capacitor. If the project parts list does not specify a voltage, choose a capacitor with a rating which is greater than the project's power supply voltage. 25V is a sensible minimum for most battery circuits. 2. Tantalum Bead Capacitors: polarized have low voltage ratings like electrolytic capacitors expensive but very small used where a large capacitance is needed in a small size. Modern tantalum bead capacitors are printed with their capacitance, voltage and polarity in full. Older ones use a color-code system which has two stripes (for the two digits) a spot of color for the number of zeros gives the value in µf. The standard color code is used for colors For the spot, grey is used to mean 0.01 white means 0.1 so that values of less than 10µF can be shown. A third color stripe near the leads shows the voltage (yellow 6.3V, black 10V, green 16V, blue 20V, grey 25V, white 30V, pink 35V). The positive (+) lead is to the right when the spot is facing you when the spot is in sight, the positive is to the right'. Examples: blue, grey, black spot means 68µF blue, grey, white spot means 6.8µF blue, grey, grey spot means 0.68µF UNPOLARISED CAPACITORS (SMALL VALUES, UP TO 1µF) Examples: Circuit symbol: Small value capacitors are unpolarised and may be connected either way round. They are not damaged by heat when soldering, except for one unusual type (polystyrene). They have high voltage ratings of at least 50V, usually 250V or so. It can be difficult to find the values of these PART I PAGE 8

13 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL small capacitors because there are many types of them and several different labelling systems! Many small value capacitors have their value printed but without a multiplier, so you need to use experience to work out what the multiplier should be! For example 0.1 means 0.1µF = 100nF. Sometimes the multiplier is used in place of the decimal point: For example: 4n7 means 4.7nF. Capacitor Number Code A number code is often used on small capacitors where printing is difficult: the 1st number is the 1st digit, the 2nd number is the 2nd digit, the 3rd number is the number of zeros to give the capacitance in pf. Ignore any letters - they just indicate tolerance and voltage rating. For example: 102 means 1000pF = 1nF (not 102pF!) For example: 472J means 4700pF = 4.7nF (J means 5% tolerance). Capacitor Color Code A color code was used on polyester capacitors for many years. It is now obsolete, but of course there are many still around. The colors should be read like the resistor code, the top three color bands giving the value in pf. Ignore the 4th band (tolerance) and 5th band (voltage rating). For example: brown, black, orange means 10000pF = 10nF = 0.01µF. Note that there are no gaps between the colour bands, so 2 identical bands actually appear as a wide band. For example:wide red, yellow means 220nF = 0.22µF. Polystyrene Capacitors This type is rarely used now. Their value (in pf) is normally printed without units. Polystyrene capacitors can be damaged by heat when soldering (it melts the polystyrene!) so you should use a heat sink (such as a crocodile clip). Clip the heat sink to the lead between the capacitor and the joint. Colour Code Colour Number Black 0 Brown 1 Red 2 Orange 3 Yellow 4 Green 5 Blue 6 Violet 7 Grey 8 White 9 Real capacitor values (the E3 and E6 series) You may have noticed that capacitors are not available with every possible value, for example 22µF and 47µF are readily available, but 25µF and 50µF are not! Why is this? Imagine that you decided to make capacitors every 10µF giving 10, 20, 30, 40, 50 and so on. That seems fine, but what happens when you reach 1000? It would be pointless to make 1000, 1010, 1020, 1030 and so on because for these values 10 is a very small difference, too small to be noticeable in most circuits and capacitors cannot be made with that accuracy. To produce a sensible range of capacitor values you need to increase the size of the 'step' as the value increases. The standard capacitor values are based on this idea and they form a series which follows the same pattern for every multiple of ten. PART I PAGE 9

14 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL The E3 series (3 values for each multiple of ten) 10, 22, 47,... then it continues 100, 220, 470, 1000, 2200, 4700, etc. Notice how the step size increases as the value increases (values roughly double each time). The E6 series (6 values for each multiple of ten) 10, 15, 22, 33, 47, 68,... then it continues 100, 150, 220, 330, 470, 680, 1000 etc. Notice how this is the E3 series with an extra value in the gaps. The E3 series is the one most frequently used for capacitors because many types cannot be made with very accurate values. Variable capacitors Variable capacitors are mostly used in radio tuning circuits and they are sometimes called 'tuning capacitors'. They have very small capacitance values, typically between 100pF and 500pF (100pF = µF). The type illustrated usually has trimmers built in (for making small adjustments - see below) as well as the main variable capacitor. Variable Capacitor Symbol Variable capacitors are not normally used in timing circuits because their capacitance is too small to be practical and the range of values available is very limited. Instead timing circuits use a fixed capacitor and a variable resistor if it is necessary to vary the time period. Variable Capacitor Trimmer capacitors: Trimmer capacitors (trimmers) are miniature variable capacitors. They are designed to be mounted directly onto the circuit board and adjusted only when the circuit is built. A small screwdriver or similar tool is required to adjust trimmers. The process of adjusting them requires patience because the presence of your hand and the tool will slightly change the capacitance of the circuit in the region of the trimmer! Trimmer capacitors are only available with very small capacitances, normally less than 100pF. It is impossible to reduce their capacitance to zero, so they are usually specified by their minimum and maximum values, for example 2-10pF. Trimmer capacitor Trimmer Capacitor Symbol PART I PAGE 10

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17 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL SWITCHES There are three important features to consider when selecting a switch: Contacts (e.g. single pole, double throw) Ratings (maximum voltage and current) Method of Operation (toggle, slide, key etc.) Circuit symbol for a simple on-off switch Switch Contacts Several terms are used to describe switch contacts: Pole - number of switch contact sets. Throw - number of conducting positions, single or double. Way - number of conducting positions, three or more. Momentary - switch returns to its normal position when released. Open - off position, contacts not conducting. Closed - on position, contacts conducting, there may be several on positions. For example: the simplest on-off switch has one set of contacts (single pole) and one switching position which conducts (single throw). The switch mechanism has two positions: open (off) and closed (on), but it is called 'single throw' because only one position conducts. Switch Contact Ratings Switch contacts are rated with a maximum voltage and current, and there may be different ratings for AC and DC. The AC values are higher because the current falls to zero many times each second and an arc is less likely to form across the switch contacts. For low voltage electronics projects the voltage rating will not matter, but you may need to check the current rating. The maximum current is less for inductive loads (coils and motors) because they cause more sparking at the contacts when switched off. PART I PAGE 13

18 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL Standard Switches Type of Switch Circuit Symbol Example ON-OFF Single Pole, Single Throw = SPST A simple on-off switch. This type can be used to switch the power supply to a circuit. When used with mains electricity this type of switch must be in the live wire, but it is better to use a DPST switch to isolate both live and neutral. (ON)-OFF Push-to-make = SPST Momentary A push-to-make switch returns to its normally open (off) position when you release the button. This is the standard doorbell switch. ON-(OFF) Push-to-break = SPST Momentary A push-to-break switch returns to its normally closed (on) position when you release the button. ON-ON Single Pole, Double Throw = SPDT This switch can be on in both positions, switching on a separate device in each case. It is often called a changeover switch. For example, a SPDT switch can be used to switch on a red lamp in one position and a green lamp in the other position. SPST toggle switch Push-to-make switch Push-to-break switch SPDT toggle switch A SPDT toggle switch may be used as a simple onoff switch by connecting to COM and one of the A or B terminals shown in the diagram. A and B are interchangeable so switches are usually not labelled. ON-OFF-ON SPDT Centre Off A special version of the standard SPDT switch. It has a third switching position in SPDT slide switch (PCB mounting) PART I PAGE 14

19 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL the centre which is off. Momentary (ON)- OFF-(ON) versions are also available where the switch returns to the central off position when released. Dual ON-OFF Double Pole, Single Throw = DPST SPDT rocker switch A pair of on-off switches which operate together (shown by the dotted line in the circuit symbol).a DPST switch is often used to switch mains electricity because it can isolate both the live and neutral connections. Dual ON-ON Double Pole, Double Throw = DPDT DPST rocker switch A pair of on-on switches which operate together (shown by the dotted line in the circuit symbol). A DPDT switch can be wired up as a reversing switch for a motor as shown in the diagram. ON-OFF-ON DPDT Centre Off A special version of the standard SPDT switch. It has a third switching position in the centre which is off. This can be very useful for motor control because you have forward, off and reverse positions. Momentary (ON)-OFF-(ON) versions are also available where the switch returns to the central off position when released. DPDT slide switch Wiring for Reversing Switch PART I PAGE 15

20 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL Special Switches Type of Switch Push-Push Switch (e.g. SPST = ON-OFF) Example This looks like a momentary action push switch but it is a standard on-off switch: push once to switch on, push again to switch off. This is called a latching action. Microswitch (usually SPDT = ON-ON) Microswitches are designed to switch fully open or closed in response to small movements. They are available with levers and rollers attached. Keyswitch A key operated switch. The example shown is SPST. Tilt Switch (SPST) Tilt switches contain a conductive liquid and when tilted this bridges the contacts inside, closing the switch. They can be used as a sensor to detect the position of an object. Some tilt switches contain mercury which is poisonous. Reed Switch (usually SPST) The contacts of a reed switch are closed by bringing a small magnet near the switch. They are used in security circuits, for example to check that doors are closed. Standard reed switches are SPST (simple on-off) but SPDT (changeover) versions are also available. PART I PAGE 16

21 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL DIP Switch (DIP = Dual In-line Parallel) This is a set of miniature SPST on-off switches, the example shown has 8 switches. The package is the same size as a standard DIL (Dual In-Line) integrated circuit. This type of switch is used to set up circuits, e.g. setting the code of a remote control. Multi-pole Switch The picture shows a 6-pole double throw switch, also known as a 6-pole changeover switch. It can be set to have momentary or latching action. Latching action means it behaves as a push-push switch, push once for the first position, push again for the second position etc. Multi-way Switch Multi-way switches have 3 or more conducting positions. They may have several poles (contact sets). A popular type has a rotary action and it is available with a range of contact arrangements from 1-pole 12-way to 4-pole 3 way. Multi-way rotary switch The number of ways (switch positions) may be reduced by adjusting a stop under the fixing nut. For example if you need a 2-pole 5-way switch you can buy the 2-pole 6-way version and adjust the stop. Contrast this multi-way switch (many switch positions) with the multi-pole switch (many contact sets) described above. 1-pole 4-way switch symbol PART I PAGE 17

22 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL RELAYS A relay is an electrically operated switch. Current flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch contacts. The coil current can be on or off. So relays have two switch positions and they are double throw (changeover) switches. Circuit symbol for a relay Relays allow one circuit to switch a second circuit which can be completely separate from the first. For example a low voltage battery circuit can use a relay to switch a 230V AC mains circuit. There is no electrical connection inside the relay between the two circuits; the link is magnetic and mechanical. The coil of a relay passes a relatively large current, typically 30mA for a 12V relay, but it can be as much as 100mA for relays designed to operate from lower voltages. Relays are usuallly SPDT or DPDT but they can have many more sets of switch contacts, for example relays with 4 sets of changeover contacts are readily available. The Relay coils produce brief high voltage 'spikes' when they are switched off and this can destroy transistors and ICs in the circuit. To prevent damage you must connect a protection diode across the relay coil. Advantages of relays over transistors: Relays can switch AC and DC, transistors can only switch DC. Relays can switch high voltages, transistors cannot. Relays are a better choice for switching large currents (> 5A). Relays can switch many contacts at once. Disadvantages of relays: Relays are bulkier than transistors for switching small currents. Relays cannot switch rapidly (except reed relays), transistors can switch many times per second. Relays use more power due to the current flowing through their coil. Relays require more current than many ICs can provide, so a low power transistor may be needed to switch the current for the relay's coil. PART I PAGE 18

23 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL BREADBOARD A breadboard is used to make up temporary circuits for testing or to try out an idea. No soldering is required so it is easy to change connections and replace components. Parts will not be damaged so they will be available to re-use afterwards. The photograph shows a typical small breadboard which is suitable for beginners building simple circuits with one or two ICs (chips). Larger sizes are available and you may wish to buy one of these to start with. Connections on Breadboard Small Breadboard Breadboards have many tiny sockets (called 'holes') arranged on a 0.1" grid. The leads of most components can be pushed straight into the holes. ICs are inserted across the central gap with their notch or dot to the left. Wire links can be made with single-core plastic-coated wire of 0.6mm diameter (the standard size). Stranded wire is not suitable because it will crumple when pushed into a hole and it may damage the board if strands break off. The diagram shows how the breadboard holes are connected: The top and bottom rows are linked horizontally all the way across as shown by the red and black lines on the diagram. The power supply is connected to these rows, + at the top and 0V (zero volts) at the bottom. Note:We can use the upper row of the bottom pair for 0V and use the lower row for the negative supply with circuits requiring a dual supply (e.g. +9V, 0V, -9V). The other holes are linked vertically in blocks of 5 with no link across the centre as shown by the blue lines on the diagram. Notice that there are separate blocks of connections to each pin of ICs. Large Breadboards: On larger breadboards there may be a break halfway along the top and bottom power supply rows. It is a good idea to link across the gap before you start to build a circuit, otherwiseyou may forget and part of your circuit will have no power! PART I PAGE 19

24 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL DIODES Diodes allow electricity to flow in only one direction. The arrow of the circuit symbol shows the direction in which the current can flow. Ordinary diodes can be split into two types: Signal diodes which pass small currents of 100mA or less and Rectifier diodes which can pass large currents. In addition there are LEDs, Zener diodes Example: Circuit symbol: Connecting and soldering Diodes must be connected the correct way round, the diagram may be labelled a or + for anode and k or - for cathode. The cathode is marked by a line painted on the body. Diodes are labelled with their code in small print, you may need a magnifying glass to read this on small signal diodes! Small signal diodes can be damaged by heat when soldering, but the risk is small unless you are using a germanium diode (codes beginning OA...) in which case you should use a heat sink clipped to the lead between the joint and the diode body. A standard crocodile clip can be used as a heat sink. Rectifier diodes are quite robust and no special precautions are needed for soldering them. Testing diodes: Testing a diode with a DIGITAL multimeter Digital multimeters have a special setting for testing a diode, usually labelled with the diode symbol. Connect the red (+) lead to the anode and the black (-) to the cathode. The diode should conduct and the meter will display a value (usually the voltage across the diode in mv, 1000mV = 1V). Reverse the connections. The diode should NOT conduct this way so the meter will display "off the scale" (usually blank except for a 1 on the left). Signal diodes (small current) Signal diodes are used to process information (electrical signals) in circuits, so they are only required to pass small currents of up to 100mA. General purpose signal diodes such as the 1N4148 are made from silicon and have a forward voltage drop of 0.7V. Germanium diodes such as the OA90 have a lower forward voltage drop of 0.2V and this makes them suitable to use in radio circuits as detectors which extract the audio signal from the weak radio signal. PART I PAGE 20

25 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL For general use, where the size of the forward voltage drop is less important, silicon diodes are better because they are less easily damaged by heat when soldering, they have a lower resistance when conducting, and they have very low leakage currents when a reverse voltage is applied. Rectifier diodes (large current) Rectifier diodes are used in power supplies to convert alternating current (AC) to direct current (DC), a process called rectification. They are also used elsewhere in circuits where a large current must pass through the diode. All rectifier diodes are made from silicon and therefore have a forward voltage drop of 0.7V. The table shows maximum current and maximum reverse voltage for some popular rectifier diodes. The 1N4001 is suitable for most low voltage circuits with a current of less than 1A. DIODE & TRANSISTOR CODING: Semi conductor diodes and transistors consist of alpha numeric code. Two letters and three figure code represents general purpose diodes. Three letters and two numbers of represent special purpose diodes. When two numbers are included in the symbol, the device is intended for industrial and professional equipment. When symbol contains three numbers, the device is intended for entertainment or consumer equipment. In case of diodes for special applications, third letter does not have any particular significance. Meaning of First Letter: A - Germanium B - Silicon C - Gallium Aresenide D - Photo Diode Meaning of Second Letter: A - General purpose diode B - tuning (Varicap diode) C - AF low powered transistor D - AF power transistor E - Tunnel diode F - HF low power transistor G - Multiple device H - Magnetic sensitive device K - Hall effect device L - HF power transistor M - Hall effect modulator P - Radiation sensitive diode (photo voltaic diode) Q - Radiation generating diode (Light emitting diode) R - Thyristor PART I PAGE 21

26 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL T - Controlled rectifier U - Power switching transistor X - Varactor diode Y - Power Rectif ier Z - Zener diode Zener diodes: a = anode, k =cathode symbol Zener diodes are used to maintain a fixed voltage. They are designed to 'breakdown' in a reliable and non-destructive way so that they can be used in reverse to maintain a fixed voltage across their terminals. The diagram shows how they are connected, with a resistor in series to limit the current. Zener diodes can be distinguished from ordinary diodes by their code and breakdown voltage which are printed on them. Zener diode codes begin BZX... or BZY... Their breakdown voltage is printed with V in place of a decimal point, so 4V7 means 4.7V for example. Zener diodes are rated by their breakdown voltage and maximum power: The minimum voltage available is 2.4V. Power ratings of 400mW and 1.3W are common. PART I PAGE 22

27 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL TRANSISTORS Transistors amplify current, for example they can be used to amplify the small output current from a logic IC so that it can operate a lamp, relay or other high current device. In many circuits a resistor is used to convert the changing current to a changing voltage, so the transistor is being used to amplify voltage. A transistor may be used as a switch (either fully on with maximum current, or fully off with no current) and as an amplifier (always partly on). The amount of current amplification is called the current gain, symbol h FE. Types of transistor There are two types of standard transistors, NPN and PNP, with different circuit symbols. The letters refer to the layers of semiconductor material used to make the transistor. Most transistors used today are NPN because this is the easiest type to make from silicon. If you are new to electronics it is best to start by learning how to use NPN transistors. The leads are labelled base (B), collector (C) and emitter (E). Transistor circuit symbols Connecting Transistors have three leads which must be connected the correct way round. Please take care with this because a wrongly connected transistor may be damaged instantly when you switch on. The orientation of the transistor will be clear from the PCB or strip board layout diagram, otherwise you will need to refer to a supplier's catalogue to identify the leads. The drawings on the right show the leads for some of the most common case styles. Please note that transistor lead diagrams show the view from below with the leads towards you. This is the opposite of IC (chip) pin diagrams which show the view from above. Transistor leads for some common case styles. PART I PAGE 23

28 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL Testing a transistor Transistors can be damaged by heat when soldering or by misuse in a circuit. If you suspect that a transistor may be damaged there are two easy ways to test it: 1. Testing with a multimeter Use a multimeter or a simple tester (battery, resistor and LED) to check each pair of leads for conduction. Set a digital multimeter to diode test and an analogue multimeter to a low resistance range. Test each pair of leads both ways (six tests in total): The base-emitter (BE) junction should behave like a diode and conduct one way only. Testing an NPN transistor The base-collector (BC) junction should behave like a diode and conduct one way only. The collector-emitter (CE) should not conduct either way. The diagram shows how the junctions behave in an NPN transistor. The diodes are reversed in a PNP transistor but the same test procedure can be used. Transistor codes There are three main series of transistor codes used in the UK: Codes beginning with B (or A), for example BC108, BC478 The first letter B is for silicon, A is for germanium (rarely used now). The second letter indicates the type; for example C means low power audio frequency; D means high power audio frequency; F means low power high frequency. The rest of the code identifies the particular transistor. There is no obvious logic to the numbering system. Sometimes a letter is added to the end (eg BC108C) to identify a special version of the main type, for example a higher current gain or a different case style. Codes beginning with TIP, for example TIP31A TIP refers to the manufacturer: Texas Instruments Power transistor. The letter at the end identifies versions with different voltage ratings. Codes beginning with 2N, for example 2N3053 The initial '2N' identifies the part as a transistor and the rest of the code identifies the particular transistor. There is no obvious logic to the numbering system. PART I PAGE 24

29 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL Choosing a transistor Most projects will specify a particular transistor, but if necessary you can usually substitute an equivalent transistor from the wide range available. The most important properties to look for are the maximum collector current I C and the current gain h FE. To make selection easier most suppliers group their transistors in categories determined either by their typical use or maximum power rating. To make a final choice you will need to consult the tables of technical data which are normally provided in catalogues. They contain a great deal of useful information but they can be difficult to understand if you are not familiar with the abbreviations used. The table below shows the most important technical data for some popular transistors, tables in catalogues and reference books will usually show additional information but this is unlikely to be useful unless you are experienced. The quantities shown in the table are explained below. NPN transistors Code Structure Case style I C max. V CE max. h FE min. P tot max. Category (typical use) Possible substitutes BC107 NPN TO18 100mA 45V mW Audio, low power BC182 BC547 BC108 NPN TO18 100mA 20V mW BC108C NPN TO18 100mA 20V mW BC109 NPN TO18 200mA 20V mW BC182 NPN TO92C 100mA 50V mW BC182L NPN TO92A 100mA 50V mW General purpose, low power General purpose, low power Audio (low noise), low power General purpose, low power General purpose, low power BC108C BC183 BC548 BC184 BC549 BC107 BC182L BC107 BC182 BC547B NPN TO92C 100mA 45V mW Audio, low power BC107B BC548B NPN BC549B NPN TO92C 100mA 30V mW TO92C 100mA 30V mW 2N3053 NPN TO39 700mA 40V mW BFY51 NPN TO39 1A 30V mW BC639 NPN TO92A 1A 80V mW TIP29A NPN TO220 1A 60V 40 30W General purpose, low power Audio (low noise), low power General purpose, low power General purpose, medium power General purpose, medium power General purpose, high power BC108B BC109 BFY51 BC639 BFY51 PART I PAGE 25

30 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL TIP31A NPN TO220 3A 60V 10 40W TIP31C NPN TO220 3A 100V 10 40W TIP41A NPN TO220 6A 60V 15 65W 2N3055 NPN TO3 15A 60V W General purpose, high power General purpose, high power General purpose, high power General purpose, high power TIP31C TIP41A TIP31A TIP41A PNP transistors Code Structure Case style I C max. V CE max. h FE min. P tot max. Category (typical use) Possible substitutes BC177 PNP TO18 100mA 45V mW Audio, low power BC477 BC178 PNP TO18 200mA 25V mW BC179 PNP TO18 200mA 20V mW General purpose, low power Audio (low noise), low power BC478 BC477 PNP TO18 150mA 80V mW Audio, low power BC177 BC478 PNP TO18 150mA 40V mW TIP32A PNP TO220 3A 60V 25 40W TIP32C PNP TO220 3A 100V 10 40W General purpose, low power General purpose, high power General purpose, high power BC178 TIP32C TIP32A PART I PAGE 26

31 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL THE SILICON CONTROLLED RECTIFIER (SCR) Shockley diodes are curious devices, but rather limited in application. Their usefulness may be expanded, however, by equipping them with another means of latching. In doing so, they become true amplifying devices (if only in an on/off mode), and we refer to them as siliconcontrolled rectifiers, or SCRs. The progression from Shockley diode to SCR is achieved with one small addition, actually nothing more than a third wire connection to the existing PNPN structure: If an SCR's gate is left floating (disconnected), it behaves exactly as a Shockley diode. A rudimentary test of SCR function, or at least terminal identification, may be performed with an ohmmeter. Because the internal connection between gate and cathode is a single PN junction, a meter should indicate continuity between these terminals with the red test lead on the gate and the black test lead on the cathode like this: All other continuity measurements performed on an SCR will show "open" ("OL" on some digital multimeter displays). It must be understood that this test is very crude and does not constitute a comprehensive assessment of the SCR. It is possible for an SCR to give good ohmmeter indications and still be defective. Ultimately, the only way to test an SCR is to subject it to a load current..if you are using a multimeter with a "diode check" function, the gate-to-cathode junction voltage indication you get may or may not correspond to what's expected of a silicon PN junction (approximately 0.7 volts). In some cases, you will read a much lower junction voltage: mere hundredths of a volt. PART I PAGE 27

32 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL UNI-JUNCTION TRANSISTOR (UJT) The Uni-junction Transistor is a two layer device, with but one P-N junction; it was once referred to as a double-base diode. It is a pulse generator, with the trigger signal applied at the emitter; a UJT will not conduct current until a peak voltage is reached on this trigger signal. This trigger voltage (V p ) is a fraction (, often called the intrinsic standoff ratio) of the interbase voltage (Vbb). The 2N2646 is a unijunction transistor used in general purpose, timing, sense and trigger applications. MAXIMUM RATINGS: Ic - 2.0A VCE 30V Power dissipated 300mW at Tc = 25 centigrade Tj C to +125 C Testing a UJT UJT testing is pretty easy once you know how to do it. 1) With a Digital Multimeter, set in the Ohms position, read the resistance between the Base 1 and Base 2; then reverse the meter-leads and take another reading. Regardless of the meter-lead polarity the measured resistance should approximately be equal (high resistance). 2) Now connect the negative (-) lead of the ohmmeter to the emitter of the UJT. With the positive (+) lead, measure the resistance from the emitter to Base 1 and then from the emitter to base 2. Both readings should indicate high resistance and about equal to each other. 3) Exchange the negative lead to the emitter with the positive lead. Measure with the negative lead the resistance between emitter and Base 1 and from Base 2 to emitter. Both readings should show low resistance and about equal to each other. 4) Remember that the 'B1' pin should always be connected to the load and not B2. PART I PAGE 28

33 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL FIELD EFFECT TRANSISTOR (FET) The junction gate field-effect transistor (JFET or JUGFET) is the simplest type of field effect transistor. It can be used as an electronically controlled switch or as a voltagecontrolled resistance. Electric charge flows through a semiconducting channel between "source" and "drain" terminals. By applying a reverse bias voltage to a "gate" terminal, the channel is "pinched", so that the electric current is impeded or switched off completely. The JFET is a long channel of semiconductor material doped and contains an abundance of positive charge carriers or holes (p-type), or of negative carriers or electrons (n-type). Ohmic contacts at each end form the source (S) and drain (D). A pn-junction is formed on one or both sides of the channel, or surrounding it, using a region with doping opposite to that of the channel, and biased using an ohmic gate contact (G). The JFET gate is sometimes drawn in the middle of the channel (instead of at the drain or source electrode as in these examples). This symmetry suggests that "drain" and "source" are interchangeable, so the symbol should be used only for those JFETs where they are indeed interchangeable. Officially, the style of the symbol should show the component inside a circle (representing the envelope of a discrete device). This is true in both the US and Europe. The symbol is usually drawn without the circle when drawing schematics of integrated circuits. More recently, the symbol is often drawn without its circle even for discrete devices. In every case the arrow head shows the polarity of the P-N junction formed between the channel and gate. As with an ordinary diode, the arrow points from P to N, the direction of conventional current when forward-biased. An English mnemonic is that the arrow of an N-channel device "points in". 2 -Drain 3- Gate 1 Source 4- Substrate Maximum Ratings: Drain-Source voltage, V DS 30V dc Drain-Gate voltage, V GD 30V dc Reverse Gate to source voltage, VGS = -30V dc Forward Gate current, Ig = 10mA dc Power dissipation at 25 C, P D - 300mW Temperature Range : -65 to +150 C PART I PAGE 29

34 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL HOW TO TEST FET WITH DIODE MODE? STEP-1. Connect DMM positive test lead to GATE DMM Negative test lead to DRAIN Display reading shows 0.715v DMM Negative test lead to SOURCE =display reading shows 0.703v STEP-2. Connect DMM Negative test lead to GATE DMM positive test lead to DRAIN = display OL ( OL MEANS OVER LOAD)...DMM positive test lead to SOURCE = display OL STEP-3. Connect DMM positive test lead to DRAIN DMM Negative test lead to SOURCE = DISPLAY READING 0.090V Connect DMM Negative test lead to DRAIN DMM Positive test lead to SOURCE = READING 0.090v or (090 mv) Connect DMM Negative lead to Shield or case or substrate DMM Positive test lead to GATE open or open or 1 DMM positive test lead to DRAIN OL DMM READING DMM positive test lead to SOURCE OL Verification: If the DMM above reading shows the condition is GOOD. Verification: If you get reading in forward bias as 0000 or OL or 1, and in reverse bias as 0000 (or) low values the FET transistor can be FAULTY and needs replacement. PART I PAGE 30

35 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL SOLDERING GUIDE How to Solder First a few safety precautions: Never touch the element or tip of the soldering iron. They are very hot (about 400 C) and will give you a nasty burn. Take great care to avoid touching the mains flex with the tip of the iron. The iron should have a heatproof flex for extra protection. An ordinary plastic flex will melt immediately if touched by a hot iron and there is a serious risk of burns and electric shock. Always return the soldering iron to its stand when not in use. Never put it down on your workbench, even for a moment! Work in a well-ventilated area. The smoke formed as you melt solder is mostly from the flux and quite irritating. Avoid breathing it by keeping you head to the side of, not above, your work. Wash your hands after using solder. Solder contains lead which is a poisonous metal. If you are careless enough to burn yourself please read the First Aid section. Preparing the soldering iron: Place the soldering iron in its stand and plug in. The iron will take a few minutes to reach its operating temperature of about 400 C. Dampen the sponge in the stand. The best way to do this is to lift it out the stand and hold it under a cold tap for a moment, then squeeze to remove excess water. It should be damp, not dripping wet. Wait a few minutes for the soldering iron to warm up. You can check if it is ready by trying to melt a little solder on the tip. Wipe the tip of the iron on the damp sponge. This will clean the tip. Melt a little solder on the tip of the iron. This is called 'tinning' and it will help the heat to flow from the iron's tip to the joint. It only needs to be done when you plug in the iron, and occasionally while soldering if you need to wipe the tip clean on the sponge. PART I PAGE 31

36 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL You are now ready to start soldering: Hold the soldering iron like a pen, near the base of the handle. Imagine you are going to write your name! Remember to never touch the hot element or tip. Touch the soldering iron onto the joint to be made. Make sure it touches both the component lead and the track. Hold the tip there for a few seconds and... Feed a little solder onto the joint. It should flow smoothly onto the lead and track to form a volcano shape as shown in the diagram. Apply the solder to the joint, not the iron. Remove the solder, then the iron, while keeping the joint still. Allow the joint a few seconds to cool before you move the circuit board. Inspect the joint closely. It should look shiny and have a 'volcano' shape. If not, you will need to reheat it and feed in a little more solder. This time ensure that both the lead and track are heated fully before applying solder. If you are careless enough to burn yourself please read the First Aid section. Using a heat sink Some components, such as transistors, can be damaged by heat when soldering so if you are not an expert it is wise to use a heat sink clipped to the lead between the joint and the component body. You can buy a special tool, but a standard crocodile clip works just as well and is cheaper. Soldering Advice for Components Crocodile clip It is very tempting to start soldering components onto the circuit board straight away, but please take time to identify all the parts first. You are much less likely to make a mistake if you do this! 1. Stick all the components onto a sheet of paper using sticky tape. PART I PAGE 32

37 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL 2. Identify each component and write its name or value beside it. 3. Add the code (R1, R2, C1 etc.) if necessary. Many projects from books and magazines label the components with codes (R1, R2, C1, D1 etc.) and you should use the project's parts list to find these codes if they are given. 4. Resistor values can be found using the resistor colour code which is explained on our Resistors page. You can print out and make your own Resistor Colour Code Calculator to help you. 5. Capacitor values can be difficult to find because there are many types with different labelling systems! The various systems are explained on our Capacitors page. 6. Some components require special care when soldering. Many must be placed the correct way round and a few are easily damaged by the heat from soldering. Appropriate warnings are given in the table below, together with other advice which may be useful when soldering. 7. For most projects it is best to put the components onto the board in the order given below: 1 Components Pictures Reminders and Warnings IC Holders (DIL sockets) 2 Resistors 3 4 Small value capacitors (usually less than 1µF) Electrolytic capacitors (1µF and greater) 5 Diodes 6 LEDs Connect the correct way round by making sure the notch is at the correct end. No special precautions are needed with resistors. These may be connected either way round. Take care with polystyrene capacitors because they are easily damaged by heat. Connect the correct way round. They will be marked with a + or - near one lead. Connect the correct way round. Take care with germanium diodes (e.g. OA91) because they are easily damaged by heat. Connect the correct way round. The diagram may be labelled a or + for anode and k or - for cathode; The cathode is the short lead and there may be a slight flat on the body of round LEDs. PART I PAGE 33

38 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL 7 Transistors Wire Links between points on the circuit board. Battery clips, buzzers and other parts with their own wires Wires to parts off the circuit board, including switches, relays, variable resistors and loudspeakers. 11 ICs (chips) single core wire stranded wire Connect the correct way round. Transistors have 3 'legs' (leads) so extra care is needed to ensure the connections are correct. Easily damaged by heat. Use single core wire, this is one solid wire which is plasticcoated. If there is no danger of touching other parts you can use tinned copper wire, this has no plastic coating and looks just like solder but it is stiffer. Connect the correct way round. You should use stranded wire which is flexible and plasticcoated. Do not use single core wire because this will break when it is repeatedly flexed. Connect the correct way round. Many ICs are static sensitive. Leave ICs in their antistatic packaging until you need them, then earth your hands by touching a metal water pipe or window frame before touching the ICs. Carefully insert ICs in their holders: make sure all the pins are lined up with the socket then push down firmly with your thumb. What is solder? Solder is an alloy (mixture) of tin and lead, typically 60% tin and 40% lead. It melts at a temperature of about 200 C. Coating a surface with solder is called 'tinning' because of the tin content of solder. Lead is poisonous and you should always wash your hands after using solder. Reels of solder Solder for electronics use contains tiny cores of flux, like the wires inside a mains flex. The flux is corrosive, like an acid, and it cleans the metal surfaces as the solder melts. This is why you must melt the solder actually on the joint, not on the iron tip. Without flux most joints would fail because metals quickly oxidise and the solder itself will not flow properly onto a dirty, oxidised, metal surface. The best size of solder for electronics is 22swg (swg = standard wire gauge). PART I PAGE 34

39 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL Desoldering At some stage you will probably need to desolder a joint to remove or re-position a wire or component. There are two ways to remove the solder: Solder 1. With a desoldering pump (solder sucker) Using a desoldering pump (solder sucker) Set the pump by pushing the spring-loaded plunger down until it locks. Apply both the pump nozzle and the tip of your soldering iron to the joint. Wait a second or two for the solder to melt. Then press the button on the pump to release the plunger and suck the molten solder into the tool. Repeat if necessary to remove as much solder as possible. The pump will need emptying occasionally by unscrewing the nozzle. 2. With solder remover wick (copper braid) Apply both the end of the wick and the tip of your soldering iron to the joint. As the solder melts most of it will flow onto the wick, away from the joint. Remove the wick first, then the soldering iron. Cut off and discard the end of the wick coated with solder. Solder remover wick After removing most of the solder from the joint(s) you may be able to remove the wire or component lead straight away (allow a few seconds for it to cool). If the joint will not come apart easily apply your soldering iron to melt the remaining traces of solder at the same time as pulling the joint apart, taking care to avoid burning yourself. PART I PAGE 35

40 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL First Aid for Burns Most burns from soldering are likely to be minor and treatment is simple: Immediately cool the affected area under gently running cold water. Keep the burn in the cold water for at least 5 minutes (15 minutes is recommended). If ice is readily available this can be helpful too, but do not delay the initial cooling with cold water. Do not apply any creams or ointments. The burn will heal better without them. A dry dressing, such as a clean handkerchief, may be applied if you wish to protect the area from dirt. Seek medical attention if the burn covers an area bigger than your hand. To reduce the risk of burns: Always return your soldering iron to its stand immediately after use. Allow joints and components a minute or so to cool down before you touch them. Never touch the element or tip of a soldering iron unless you are certain it is cold. PART I PAGE 36

41 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL MULTIMETERS Multimeters are very useful test instruments. By operating a multi-position switch on the meter they can be quickly and easily set to be Liquid-Crystal Display a voltmeter, an ammeter or an ohmmeter. They have several settings (LCD) (called 'ranges') for each type of meter and the choice of AC or DC. Some multimeters have additional features such as transistor testing and ranges for measuring capacitance and frequency. Choosing a multimeter The photographs below show modestly priced multimeters which are suitable for general electronics use, you should be able to buy meters like these for less than 15. A digital multimeter is the best choice for your first multimeter, even the cheapest will be suitable for testing simple projects. If you are buying an analogue multimeter make sure it has a high sensitivity of 20k /V or greater on DC voltage ranges, anything less is not suitable for electronics. The sensitivity is normally marked in a corner of the scale, ignore the lower AC value (sensitivity on AC ranges is less important), the higher DC value is the critical one. Beware of cheap analogue multimeters sold for electrical work on cars because their sensitivity is likely to be too low. Digital multimeters All digital meters contain a battery to power the display so they use virtually no power from the circuit under test. This means that on their DC voltage ranges they have a very high resistance (usually called input impedance) of 1M or more, usually 10M, and they are very unlikely to affect the circuit under test. Typical ranges for digital multimeters like the one illustrated: (the values given are the maximum reading on each range) DC Voltage: 200mV, 2000mV, 20V, 200V, 600V. AC Voltage: 200V, 600V. DC Current: 200µA, 2000µA, 20mA, 200mA, 10A*. *The 10A range is usually unfused and connected via a special socket. AC Current: None. (You are unlikely to need to measure this). Resistance: 200, 2000, 20k, 200k, 2000k, Diode test. Digital Multimeter Digital meters have a special diode test setting because their resistance ranges cannot be used to test diodes and other semiconductors. PART I PAGE 37

42 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL Analogue multimeters Analogue meters take a little power from the circuit under test to operate their pointer. They must have a high sensitivity of at least 20k /V or they may upset the circuit under test and give an incorrect reading. See the section below on sensitivity for more details. Batteries inside the meter provide power for the resistance ranges, they will last several years but you should avoid leaving the meter set to a resistance range in case the leads touch accidentally and run the battery flat. Typical ranges for analogue multimeters like the one illustrated: (the voltage and current values given are the maximum reading on each range) DC Voltage: 0.5V, 2.5V, 10V, 50V, 250V, 1000V. AC Voltage: 10V, 50V, 250V, 1000V. DC Current: 50µA, 2.5mA, 25mA, 250mA. A high current range is often missing from this type of meter. AC Current: None. (You are unlikely to need to measure this). Resistance: 20, 200, 2k, 20k, 200k. These resistance values are in the middle of the scale for each range. Analogue Multimeter It is a good idea to leave an analogue multimeter set to a DC voltage range such as 10V when not in use. It is less likely to be damaged by careless use on this range, and there is a good chance that it will be the range you need to use next anyway! Sensitivity of an analogue multimeter Multimeters must have a high sensitivity of at least 20k /V otherwise their resistance on DC voltage ranges may be too low to avoid upsetting the circuit under test and giving an incorrect reading. To obtain valid readings the meter resistance should be at least 10 times the circuit resistance (take this to be the highest resistor value near where the meter is connected). You can increase the meter resistance by selecting a higher voltage range, but this may give a reading which is too small to read accurately! On any DC voltage range: Analogue Meter Resistance = Sensitivity Max. reading of range A meter with 20k /V sensitivity on its 10V range has a resistance of 20k /V 10V = 200k. By contrast, digital multimeters have a constant resistance of at least 1M (often 10M ) on all their DC voltage ranges. This is more than enough for almost all circuits. Measuring voltage and current with a multimeter 1. Select a range with a maximum greater than you expect the reading to be. 2. Connect the meter, making sure the leads are the correct way round. Digital meters can be safely connected in reverse, but an analogue meter may be damaged. 3. If the reading goes off the scale: immediately disconnect and select a higher range. PART I PAGE 38

43 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL Multimeters are easily damaged by careless use so please take these precautions: Always disconnect the multimeter before adjusting the range switch. Always check the setting of the range switch before you connect to a circuit. Never leave a multimeter set to a current range (except when actually taking a reading). The greatest risk of damage is on the current ranges because the meter has a low resistance. Voltage at a point really means the voltage difference between that point and 0V (zero volts) which is normally the negative terminal of the battery or power supply. Usually 0V will be labelled on the circuit diagram as a reminder. Reading analogue scales Check the setting of the range switch and choose an appropriate scale. For some ranges you may need to multiply or divide by 10 or 100 as shown in the sample readings below. For AC voltage ranges use the red markings because the calibration of the scale is slightly different. Sample readings on the scales shown: DC 10V range: 4.4V (read 0-10 scale Analogue Multimeter Scales directly) These can appear daunting at first but remember DC 50V range: 22V (read 0-50 scale directly) that you only need to read one scale at a time! DC 25mA range: 11mA (read and The top scale is used when measuring resistance. divide by 10) AC 10V range: 4.45V (use the red scale, reading 0-10) Measuring resistance with a multimeter To measure the resistance of a component it must not be connected in a circuit. If you try to measure resistance of components in a circuit you will obtain false readings (even if the supply is disconnected) and you may damage the multimeter. The techniques used for each type of meter are very different so they are treated separately: Measuring resistance with a DIGITAL multimeter 1. Set the meter to a resistance range greater than you expect the resistance to be. Notice that the meter display shows "off the scale" (usually blank except for a 1 on the left). Don't worry, this is not a fault, it is correct - the resistance of air is very high! 2. Touch the meter probes together and check that the meter reads zero. If it doesn't read zero, turn the switch to 'Set Zero' if your meter has this and try again. 3. Put the probes across the component. Avoid touching more than one contact at a time or your resistance will upset the reading! PART I PAGE 39

44 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL Measuring resistance with an ANALOGUE multimeter The resistance scale on an analogue meter is normally at the top, it is an unusual scale because it reads backwards and is not linear (evenly spaced). This is unfortunate, but it is due to the way the meter works. 1. Set the meter to a suitable resistance range. Choose a range so that the resistance you expect will be near the middle of the scale. For example: with the scale shown below and an expected resistance of about 50k choose the 1k range. 2. Hold the meter probes together and adjust the control on the front of the meter which is usually labelled "0 ADJ" until the pointer reads zero (on the RIGHT remember!). If you can't adjust it to read zero, the battery inside the meter needs replacing. 3. Put the probes across the component. Avoid touching more than one contact at a time or your resistance will upset the reading! Reading analogue resistance scales For resistance use the upper scale, noting that it reads backwards and is not linear (evenly spaced). Check the setting of the range switch so that you know by how much to multiply the reading. Sample readings on the scales shown: 10 range: 260 1k range: 26k Analogue Multimeter Scales The resistance scale is at the top, note that it reads backwards and is not linear (evenly spaced). Testing a diode with an ANALOGUE multimeter Set the analogue multimeter to a low value resistance range such as 10. It is essential to note that the polarity of analogue multimeter leads is reversed on the resistance ranges, so the black lead is positive (+) and the red lead is negative (-)! This is unfortunate, but it is due to the way the meter works. Connect the black (+) lead to anode and the red (-) to the cathode. The diode should conduct and the meter will display a low resistance (the exact value is not relevant). Reverse the connections. The diode should NOT conduct this way so the meter will show infinite resistance (on the left of the scale). PART I PAGE 40

45 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL Testing a transistor with a multimeter Set a digital multimeter to diode test and an analogue multimeter to a low resistance range such as 10, as described above for testing a diode. Test each pair of leads both ways (six tests in total): The base-emitter (BE) junction should behave like a diode and conduct one way only. The base-collector (BC) junction should behave like a diode and conduct one way only. The collector-emitter (CE) should not conduct either way. Testing an NPN transistor The diagram shows how the junctions behave in an NPN transistor. The diodes are reversed in a PNP transistor but the same test procedure can be used. Some multimeters have a 'transistor test' function, please refer to the instructions supplied with the meter for details. PART I PAGE 41

46 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL FUNCTION GENERATOR A signal generator that delivers different Waveforms for a wide frequency range is referred to as FUNCTION GENERATOR. They are commercially available as a Complete Test Instrument. The Variety of the Wave Shapes provided generally determines the complexity and cost of the Function Generator. The basic Waveforms produced by most Function Generators are Square and Triangular. These Waveforms can be shaped by Non-Linear Amplifiers to produce a variety of other waveforms including a Sinusoidal Waveforms. There are 2 basic functions performed by the waveform generator System. A capacitor charging used to fix Waveforms periods and Generate a Triangular Waveform, and a Comparator function used to sense Capacitor voltage and switch between charge and discharge conditions. In the Function Generator the basic waveform is Triangular Waveform and is produced by an Active Integrator and other Waveforms are derived from the basic triangular waveform. The FG has a decided advantage over the conventional Signal sources TECHNICAL DATA: Power : 230volts AC,+/-10%,50Hz Waveforms : Sine, Square, Triangle and Pulse Amplitude : 0-20Vpp (5volt fixed for TTL Output) Sine Wave Distotion : Less than 1% Frequency Range : 0.1Hz - 1MHz Output Impedance : 600 ohms and 50 ohms Switch Selectable Output ShortCKT protection : Indefinite Output Coupling : DC Coupling Square Wave Duty Cycle : 49% to 51% Square Wave Rise Time (TTL): Less than 25 Nanoseconds. Attenuation : 10dB, 20dB, 40dB are provided VCO in : Input through Bs2 connector for Frequency Modulation Techniques. DC Offset : 0 to +/- 10volt continuously Variable Output Termination : 1.Binding terminals for frequency output PART I PAGE 42

47 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL 2.Binding terminals for TTL output Frequency readout : 5 digit frequency counter INT /EXT : switch is provided for internal and external frequency EXT input : binding terminal is provided to feed external input for counter Width : Duty Cycle of TTL can be varied in square wave Weight : Aproximately 2Kgs Size : 240(W)*90(H)) 230(D)mm OPERATING INSTRUCTION This provides first time operation for a function generator.if unfamiliar to operate this instrument, operate the instrument as per the procedure given below until all controls are clearly known. OPERATING PROCEDURE:- Initially set all the controls as stated below. POWER ON : Off (Release) RANGE : 10K (Depress) FUNCTION : Sine (Depress) DC OFFSET : Off (Fully anti clockwise) ATTENUATOR : 0dB (Release) COUNTER : Switch selected to INT position. AMPLITUDE : Fully clockwise EXT/INT : INT position Insert 3-pin plug of main chord into 230V AC mains socket with proper earthen. Press POWER ON switch, display will glow indicating the instrument is ON position. Allow the instrument to warm up for a period of few minutes. Observe the output via.. output terminal in CRO. PART I PAGE 43

48 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL FREQUENCY:- For setting the frequency of waveform, depress the particular range selector push button. Observe the decimal point on display. It is positioned automatically to give the direct frequency reading in KHz. For eg., 1. To set frequency of 5Hz, depress the20 push button and adjust fine frequency until display reads KHz. 2. To set frequency of 50Hz, depress the 200 push button and adjust fine frequency until display reads KHz. 3. To set frequency of 200Hz, depress 2K push button and adjust fine frequency until display reads KHz. 4. To set frequency of 2 KHz, depress 20K push button and adjust fine frequency until display reads KHz. 5. To set frequency of 70 KHz, depress 200K push button and adjust fine frequency until display reads KHz. 6. To set frequency of 2 MHz, depress 2M push button and adjust fine frequency until display reads KHz FUNCTION:- Depress respective function button to observe sine, square, triangle waveforms in CRO. ATTENUATOR:- 1. Sine Function 2. Square Function 3. Triangular Function Attenuator push buttons with amplitude control enables output to any desired level. Press Attenuator push buttons to have 10dB, 20dB, 40dB attenuated signal. The amplitude control knob controls the amplitude level of output signal. OUTPUT:- The desired signal can be observed through OUTPUT terminal with respect to ground provided with impedance of 50 ohms and 600 ohms through push button. DC OFFSET:- Rotate Dc Offset clockwise to ON. This knob can be used to clip the waveform both in positive and negative direction. At higher signal amplitudes notice the clipping of waveform. PART I PAGE 44

49 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL VCO IN:- This terminal is used for frequency modulation. By applying 50Hz frequency signal with minimum amplitude for external source to VCO IN and set function generator to 1KHz of required amplitude. Now observe the output, it is combination of two frequency components. This leads to FM output. TTL:- Square wave (TTL) of fixed 5Vp-p amplitude with selected frequency can be observed at this terminal when connected to CRO. INT/EXT: This switch facility is provided in order to read internal and external applied frequency. Selection of INT switch will facilitate frequency counter to read the internally generated frequency. Selection of EXT switch will facilitate frequency counter to read externally fed frequency to EXTIN terminal. The frequency can count up to 3MHz. WIDTH:- Select square waveform using function switch and now vary the WIDTH control in clockwise direction and observe the change in width of square wave when connected to CRO. PRECAUTIONS:- The following precautions should be followed for the better performance of kit. 1. Avoid using the function generator in high temperature and humidity conditions also ensures that the instrument is from dust free. 2. Magnetic fields and mechanical vibrations should be avoid while operating the function generator. 3. The function generator is extremely meant for 230V/50Hz 4. Handle the function generator carefully 5. Avoid opening the case, while the instrument is ON or OFF position PART I PAGE 45

50 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL CATHODE RAY OSCILLOSCOPE (CRO) An oscilloscope is a test instrument which allows you to look at the 'shape' of electrical signals by displaying a graph of voltage against time on its screen. It is like a voltmeter with the valuable extra function of showing how the voltage varies with time. A graticule with a 1cm grid enables you to take measurements of voltage and time from the screen. Circuit symbol for an oscilloscope The graph, usually called the trace, is drawn by a beam of electrons striking the phosphor coating of the screen making it emit light, usually green or blue. This is similar to the way a television picture is produced. Oscilloscopes contain a vacuum tube with a cathode (negative electrode) at one end to emit electrons and an anode (positive electrode) to accelerate them so they move rapidly down the tube to the screen. This arrangement is called an electron gun. The tube also contains electrodes to deflect the electron beam up/down and left/right. The electrons are called cathode Cathode Ray Oscilloscope (CRO) rays because they are emitted by the cathode and this gives the oscilloscope its full name of cathode ray oscilloscope or CRO. A dual trace oscilloscope can display two traces on the screen, allowing you to easily compare the input and output of an amplifier for example. It is well worth paying the modest extra cost to have this facility. Setting up an oscilloscope Oscilloscopes are complex instruments with many controls and they require some care to set up and use successfully. It is quite easy to 'lose' the trace off the screen if controls are set wrongly! There is some variation in the arrangement and labeling of the many controls so the following instructions may need to be adapted for your instrument. 1. Switch on the oscilloscope to warm up (it takes a minute or two). 2. Do not connect the input lead at this stage. 3. Set the AC/GND/DC switch (by the Y INPUT) to DC. 4. Set the SWP/X-Y switch to SWP (sweep). 5. Set Trigger Level to AUTO. 6. Set Trigger Source to INT (internal, the y input). 7. Set the Y AMPLIFIER to 5V/cm (a moderate value). 8. Set the TIMEBASE to 10ms/cm (a moderate speed). 9. Turn the timebase VARIABLE control to 1 or CAL. This is what you should see after setting up, when there is no input signal connected PART I PAGE 46

51 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL 10. Adjust Y SHIFT (up/down) and X SHIFT (left/right) to give a trace across the middle of the screen, like the picture. 11. Adjust INTENSITY (brightness) and FOCUS to give a bright, sharp trace. 12. The oscilloscope is now ready to use! Connecting an oscilloscope The Y INPUT lead to an oscilloscope should be a co-axial lead and the diagram shows its construction. The central wire carries the signal and the screen is connected to earth (0V) to shield the signal from electrical interference (usually called noise).most oscilloscopes have a BNC socket for the y input and the lead is connected with a push and twist action, to disconnect you need to twist and pull. Oscilloscopes used in schools may have red and black 4mm sockets so that ordinary, unscreened, 4mm plug leads can be used if necessary. Professionals use a specially designed lead and probes kit for best results with high frequency signals and when testing high resistance circuits, but this is not essential for simpler work at audio frequencies (up to 20kHz). An oscilloscope is connected like a voltmeter but you must be aware that the screen (black) connection of the input lead is connected to mains earth at the oscilloscope! This means it must be connected to earth or 0V on the circuit being tested. Obtaining a clear and stable trace Once you have connected the oscilloscope to the circuit you wish to test you will need to adjust the controls to obtain a clear and stable trace on the screen: The Y AMPLIFIER (VOLTS/CM) control determines the height of the trace. Choose a setting so the trace occupies at least half the screen height, but does not disappear off the screen. The TIMEBASE (TIME/CM) control determines the rate at which the dot sweeps across the screen. Choose a setting so the trace shows at least one cycle of the signal across the screen. The TRIGGER control is usually best left set to AUTO. If you are using an oscilloscope for the first time it is best to start with an easy signal such as the output from an AC power pack set to about 4V. Construction of a co-axial lead Oscilloscope lead and probes kit The trace of an AC signal with the oscilloscope controls correctly set PART I PAGE 47

52 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL Measuring voltage and time period The trace on an oscilloscope screen is a graph of voltage against time. The shape of this graph is determined by the nature of the input signal. In addition to the properties labelled on the graph, there is frequency which is the number of cycles per second. The diagram shows a sine wave but these properties apply to any signal with a constant shape. Amplitude is the maximum voltage reached by the signal. It is measured in volts, V. Peak voltage is another name for amplitude. Peak-peak voltage is twice the peak voltage (amplitude). When reading an oscilloscope trace it is usual to measure peak-peak voltage. Time period is the time taken for the signal to complete one cycle. It is measured in seconds (s), but time periods tend to be short so milliseconds (ms) and microseconds (µs) are often used. 1ms = 0.001s and 1µs = s. Frequency is the number of cycles per second. It is measured in hertz (Hz), but frequencies tend to be high so kilohertz (khz) and megahertz (MHz) are often used. 1kHz = 1000Hz 1MHz = Hz. frequency = 1/t time period = 1/f PART I PAGE 48

53 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL The trace of an AC signal Y AMPLIFIER: 2V/cm ; TIMEBASE: 5ms/cm Example measurements: peak-peak voltage = 8.4V amplitude voltage = 4.2V time period = 20ms frequency = 50Hz Voltage Voltage is shown on the vertical y-axis and the scale is determined by the Y AMPLIFIER (VOLTS/CM) control. Usually peak-peak voltage is measured because it can be read correctly even if the position of 0V is not known. The amplitude is half the peak-peak voltage. Voltage = distance in cm volts/cm Example: peak-peak voltage = 4.2cm 2V/cm = 8.4V amplitude (peak voltage) = ½ peak-peak voltage = 4.2V S. NO No. of divisions on vertical axis a cm Volts/ division b volts Peak to Peak voltage c = a x b volts Peak voltage d= c/2 voltsw Time period Time is shown on the horizontal x-axis and the scale is determined by the TIMEBASE (TIME/CM) control. The time period (often just called period) is the time for one cycle of the signal. The frequency is the number of cyles per second, frequency = 1/time period Time = distance in cm time/cm Example: time period = 4.0cm 5ms/cm = 20ms and frequency = 1 / time period = 1 / 20ms = 50Hz PART I PAGE 49

54 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL S. NO No. of horizontal divisions a cm 1 Time/ division b volts Time period c = a x b ( ) Frequency in Hz 2 3 Timebase (time/cm) and trigger controls Slow timebase, no input You can see the dot moving The oscilloscope sweeps the electron beam across the screen from left to right at a steady speed set by the TIMEBASE control. Each setting is labelled with the time the dot takes to move 1cm, effectively it is setting the scale on the x-axis. The timebase control may be labelled TIME/CM. At slow timebase settings (such as 50ms/cm) you can see a dot moving across the screen but at faster settings (such as 1ms/cm) the dot is moving so fast that it appears to be a line. The VARIABLE timebase control can be turned to make a fine adjustment to the speed, but it must be left at the position labelled 1 or CAL (calibrated) if you wish to take time readings from the trace drawn on the screen. Fast timebase, no input The dot is too fast to see so it appears to be a line The TRIGGER controls are used to maintain a steady trace on the screen. If they are set wrongly you may see a trace drifting sideways, a confusing 'scribble' on the screen, or no trace at all! The trigger maintains a steady trace by starting the dot sweeping across the screen when the input signal reaches the same point in its cycle each time. For straightforward use it is best to leave the trigger level set to AUTO, but if you have difficulty obtaining a steady trace try adjusting this control to set the level manually. Y amplifier (volts/cm) control The oscilloscope moves the trace up and down in proportion to the Voltage at the Y INPUT and the setting of the Y AMPLIFIER control. This control sets the voltage represented by each centimetre(cm) on the the screen, effectively it is setting the scale on the y-axis. Positive voltages make the trace move up, negative voltages make it move down. The y amplifier control may be labelled Y-GAIN or VOLTS/CM. The input voltage moving the dot up and down at the same time as the dot is swept across the screen means that the trace on the screen is a graph of voltage (y-axis) against time (x-axis) for the input signal. Varying DC (always positive) PART I PAGE 50

55 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL The AC/GND/DC switch The normal setting for this switch is DC for all signals, including AC! Switching to GND (ground) connects the y input to 0V and allows you to quickly check the position of 0V on the screen (normally halfway up). There is no need to disconnect the input lead while you do this because it is disconnected internally. Switching to AC inserts a capacitor in series with the input to block out any DC signal present and pass only AC signals. This is used to examine signals showing a small variation around one constant value, such as the ripple on the output of a smooth DC supply. Reducing the VOLTS/CM to see more detail of the ripple would normally take the trace off the screen! The AC setting removes the constant (DC) part of the signal, allowing you to view just the varying (AC) part which can now be examined more closely by reducing the VOLTS/CM. This is shown in the diagrams below: Displaying a ripple signal using the AC switch Switching to GND allows you to quickly check the position of 0V (normally halfway up). Precautions An oscilloscope should be handled gently to protect its fragile (and expensive) vacuum tube. Oscilloscopes use high voltages to create the electron beam and these remain for some time after switching off - for your own safety do not attempt to examine the inside of an oscilloscope! PART I PAGE 51

56 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL REGULATED POWER SUPPLY The power supply unit is specially developed for laboratory use where low ripple and noise and high voltage regulation is to be maintained. The panel meter indicates both the voltage and current. Simultaneously the outputs are floating, current limited, self-recovery on removal of fault. This power supply employs series regulator technique. The unit operates on a supply voltage of 230V+/-10%, 50Hz, Single Phase AC ensure proper polarity and earthing before plugging the unit. OPERATING INSTRUCTIONS: Before switching the unit ON first observe the following: 1. The Input ON/OFF switch ON OFF position 2. Plug the input mains cord in appropriate socket and switch ON the ON/OFF switch. The Neon/LED will glow indicating the availability of the input supply 3. Power Supply output settings a) Voltage setting: The power supply unit has automatic cross over type of output characteristics. The cross over point is decided by the set output voltage level and set current limit. The output voltage can be set to the desired level by adjusting control on the front panel without connecting load. b) Current setting: The output current can be set by decreasing the current potentiometer to minimum position (anti clock wise); short the +ve and ve terminal (at 1VDC) and adjust required current. Remove the short circuit and load the unit. The power supply will work with in the set current limit and output voltage CIRCUIT DESCRIPTION: Low voltage is obtained by double wound step down transformer. This voltage is rectified and filtered using bridge rectifiers and capacitor input filters. Operational amplifier is used to compare any change from the set value due to line and load variations with stabilized reference voltage obtained from IC 723. Another comparator is used to monitor the load current when the load current exceeds the set current. The voltage starts dropping. This is necessary so that the power dissipation on the transistor does not exceed the safe operating area. To bring the unit into normal operation, remove/reduce the load. MAINTENANCE: 1. The transistor and semi-conductor diodes fail rarely. 2. If the mains indicator does not glow, check the fuse and mains power card. 3. If the output voltage is high but there is no control by voltage controls check the series transistors, potentiometers and ICs. 4.If the voltage is being affected by mains variation check the reference supply circuit. PART I PAGE 52

57 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL COILS An electromagnetic coil (or simply a "coil") is formed when a conductor (usually an insulated solid copper wire) is wound around a core or form to create an inductor or electromagnet. When electricity is passed through a coil, it generates a magnetic field. One loop of wire is usually referred to as a turn or a winding, and a coil consists of one or more turns. For use in an electronic circuit, electrical connection terminals called taps are often connected to a coil. Coils are often coated with varnish or wrapped with insulating tape to provide additional insulation and secure them in place. A completed coil assembly with one or more set of coils and taps is often called the windings. Windings are used in transformers, electric motors, inductors, solenoids loudspeakers, and many other applications. The conducting material used for the windings depends upon the application, but in all cases the individual turns must be electrically insulated from each other to ensure that the current travels throughout every turn. For small power and signal applications, in which currents are low and the potential difference between adjacent turns is small, the coils are often wound from enamelled magnet wire, such as Formvar wire. Larger power transformers operating at high voltages may be wound with copper rectangular strip conductors insulated by oil-impregnated paper and blocks of pressboard. TAPS: Coils may have taps at intermediate points on the winding for various uses. In transformers, taps may be manually reconnected, or a manual or automatic switch may be provided for changing taps. Automatic on-load tap changers are used in electric power transmission or distribution, on equipment such as arc furnace transformers, or for automatic voltage regulators for sensitive loads. Audio-frequency transformers, used for the distribution of audio to public address loudspeakers, have taps to allow adjustment of impedance to each speaker. A center-tapped transformer is often used in the output stage of an audio power amplifier in a push-pull circuit. PART I PAGE 53

58 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL SOLENOID: A Solenoid is a coil would into a tightly packed helix. The term was invented by Andre- Marie Ampere to designate a helical coil. In physics, the term refers specifically to a long, thin loop of wire, often wrapped around a metallic core, which produces a uniform magnetic field in a volume of space (where some experiment might be carried out) when an electric current is passed through it. Solenoids are important because they can create controlled magnetic fields and can be used as electromagnets. In engineering, the term may also refer to a variety of transducer devices that convert energy into linear motion. The term is also often used to refer to a solenoid valve, which is an integrated device containing an electromechanical solenoid which actuates either a pneumatic or hydraulic valve, or a solenoid switch, which is a specific type of relay that internally uses an electromechanical solenoid to operate an electrical switch; for example, an automobile starter solenoid, or a linear solenoid, which is an electromechanical solenoid. TRANSFORMERS: A transformer is an electromagnetic device that has a primary winding and a secondary winding that transfer energy from one electrical circuit to another by inductive coupling without moving parts. The term tickler coil usually refers to a feedback coil, which is often the third coil placed in relation to a primary coil and secondary coil. The coil tap(s) are points in a wire coil where a conductive patch has been exposed (usually on a loop of wire that extends out of the main coil body). Inductor coil An inductor coil is typically has a relatively simple two-terminal winding over a magnetic core. Electric motor Electric motor windings can be quite complex. They are often 3 phase design, with 3 sets of windings. Many different layouts, interleavings and windings are in use. PART I PAGE 54

59 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL INDUCTORS An inductor, also called a coil or reactor, is a passive two-terminal electrical component which resists changes in electric current passing through it. It consists of a conductor such as a wire, usually wound into a coil. When a current flows through it, energy is stored temporarily in a magnetic field in the coil. When the current flowing through an inductor changes, the time-varying magnetic field induces a voltage in the conductor, according to Faraday s law of electromagnetic induction, which opposes the change in current that created it. An inductor is characterized by its inductance, the ratio of the voltage to the rate of change of current, which has units of henries (H). Many inductors have a magnetic core made of iron or ferrite inside the coil, which serves to increase the magnetic field and thus the inductance. Along with capacitors and resistors, inductors are one of the three passive linear circuit elements that make up electric circuits. Inductors are widely used in alternating current (AC) electronic equipment, particularly in radio equipment. They are used to block the flow of AC current while allowing DC to pass; inductors designed for this purpose are called chokes. They are also used in electronic filters to separate signals of different frequencies, and in combination with capacitors to make tuned circuits, used to tune radio and TV receivers. APPLICATIONS: Inductors are used extensively in analog circuits and signal processing. Inductors are also employed in electrical transmission systems, where they are used to limit switching currents and fault currents. In this field, they are more commonly referred to as reactors. PART I PAGE 55

60 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL COLOUR CODING OF INDUCTORS: The color codes for inductors are identical to that of a resistor so if you are familiar with resistors this should be very easy The tricky part is remembering the results from this will be in micro Henrys, not just Henrys First break down the bands. The last band is the tolerance, and the band right before that is the multiplier. The other bands are the numbers Ex : BROWN, ORANGE, BROWN, BLACK BROWN - ORANGE - BROWN - BLACK 1 3 X10 +/-20% So we have 13 x 10 +/-20%, meaning out inductance is 130 micro Henrys with a 20 percent tolerance, or in other words, our actual inductance can be anywhere between 104 and 156 micro Henrys. PART I PAGE 56

61 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL TYPES OF INDUCTORS: Air core Inductors: The term air core coil refers to coils wound on plastic, ceramic, or other nonmagnetic forms, as well as those that have only air inside the windings. Air core coils have lower inductance than ferromagnetic core coils, but are often used at high frequencies because they are free from energy losses called core losses. Radio frequency inductors: At high frequencies, particularly radio frequencies (RF), inductors have higher resistance and other losses. In addition to causing power loss, in resonant circuits this can reduce the Q factor of the circuit, broadening the bandwidth. In RF inductors, which are mostly air core types, specialized construction techniques are used to minimize these losses. The losses are due to these effects. Basket weave coils or honey comb coils: To reduce the proximity effect and parasitic capacitance, multilayer RF coils are would in patterns in which successive turns are not parallel but crisscrossed at an angle. Spider web coils: These are often wound on a flat insulating support with radial spokes or slots, with the wire weaving in and out through the slots; these are called spiderweb coils. The form has an odd number of slots, so successive turns of the spiral lie on opposite sides of the form, increasing separation. PART I PAGE 57

62 ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL Variable Inductor: Probably the most common type of variable inductor today is one with a moveable ferrite magnetic core, which can be slid or screwed in or out of the coil. Moving the core farther into the coil increases the permeability, increasing the magnetic field and the inductance. Many inductors used in radio applications (usually less than 100 MHz) use adjustable cores in order to tune such inductors to their desired value, since manufacturing processes have certain tolerances PART I PAGE 58