Secondary school of electrical engineering. present

Transcription

1 Secondary school of electrical engineering Vlastimil Šetka, Zdeněk k Franče, Jakub Tichý,, Lucie Halasová, Petr Časta, Michal PánovecP present

2 Proposition of power supply The first information, which we need to know are output voltage and current Type of supply stabilizated or not Officil of ripple

3 Schema of power source

4 Rectifier We would to chose type of rectify: half-wave, full-wave or bridge Used type of diode are 1N4xxx, depend on max. Allowed voltage Bridge are integrated like a Gratz or made up from discrete parts

5 Proposition of filter From knowedge of officil of ripple and chosen value of induktance we can calculate capacity Most used are passive capacitor filters, can be with inductance Formula: φrip. = m 2.ω 2.L.C-1

6 Stabilizer We are restricted by voltage and current, so we choose LM 317K: Parameters: max. Input voltage 40V Current 2,2A Stabilization volume from 1,2V to 37V Regulation is implemented by linear potenciometer Diodes are used like protection against short circuit and overwork

7 Voltage loss by any parts Rectifier: 1,4V Filter: It's based on inner resistance of part and theme curent Stabilizer: 3V

8 Cooler The power loss on stabilizer is changed to warm and stabilizer could be destroyed if isn t cooled.

9 Transformers

10 Basic principles A transformer can be likened to a mechanical gearbox, which transfers mechanical energy from a high-speed, low torque shaft to a lower-speed, higher-torque shaft, but which is not a source of energy itself. A transformer transfers electrical energy from a high-current, low-voltage circuit to a lower-current, higher-voltage circuit.

11 Construction A simple transformer consists of two electrical conductors called the primary winding and the secondary winding. Energy is coupled between the windings by the time varying magnetic flux that passes through (links) both primary and secondary windings. Whenever the amount of current in a coil changes, a voltage is induced in the neighboring coil. The effect, called mutual inductance, is an example of electromagnetic induction.

12 If a time-varying voltage is applied to the primary winding of turns, a current will flow in it producing a magnetomotive force (MMF). Just as an electromotive force (EMF) drives current around an electric circuit, so MMF tries to drive magnetic flux through a magnetic circuit. The primary MMF produces a varying magnetic flux in the core, and, with an open circuit secondary winding, induces a back electromotive force (EMF) in opposition to. In accordance with Faraday's law of induction, the voltage induced across the primary winding is proportional to the rate of change of flux.

13 If the flux in the core is sinusoidal, the relationship for either winding between its number of turns, voltage, magnetic flux density and core cross-sectional area is given by the universal emf equation (from Faraday's law): where E is the sinusoidal rms or root mean square voltage of the winding, f is the frequency in hertz, N is the number of turns of wire on the winding, a is the cross-sectional area of the core in square metres B is the peak magnetic flux density in teslas

14 Operating situations idle circuit- this is situation when is not connect load to the circuit short circuit- when are the ends of the circuit short load circuit- when is the load connect

15 Circuit symbols Transformer with two windings and iron core. Transformer with three windings. The dots show the relative winding configuration of the windings. Step-down or step-up transformer. The symbol shows which winding has more turns, but does not usually show the exact ratio. Transformer with electrostatic screen, which prevents capacitive coupling between the windings.

16 Toroidal cores: Toroidal transformers are built around a ringshaped core, which is made from a long strip of silicon steel or permalloy wound into a coil, from powdered iron, or ferrite, depending on operating frequency. The strip construction improving the transformer's efficiency and also provides screening to minimize the core's magnetic field from generating electromagnetic interference

17 Rectifier What is the rectifier? Converts alternating current to direct current Power supplies: AC from transformer to needed DC Vlastimil Šetka

18 Rectifier Components Vacuum tube diodes (in history) Solid state diodes (silicon or germanium semiconductor) One or usually more diodes in specific arrangement for better efficiency bridge rectifier, several types of silicon diodes

19 Rectifier Diode parameters Forward current I FMAX Maximum peak reverse voltage U RMAX Peak voltage drop-out depends on current, above 0.7 V Maximum power loss (temperature) Part of datasheet maximum ratings for common types of diodes:

20 Rectifier Half wave rectifier Either the positive or negative half of the AC wave is passed Only 1 diode, usable only for low currents

21 Rectifier Full wave rectifier Converts both polarities of the input waveform, efficient Only 2 diodes but needs center-tapped transformer Voltage drop-out only on one diode 0.7 V

22 Rectifier Full wave bridge rectifier (Gratz bridge) Converts both polarities of the input waveform, efficient 4 diodes, doesn t need center-tapped transformer Voltage drop-out on two diodes 1,4 V bridge rectifier in one component

23 Rectifier Filter output smoothing Rectifier supplies voltage of fixed polarity but pulsating Parallel capacitor on rectifier output lessens the ripple Charge in capacitor flows out through the load while voltage on rectifier output is smaller than on capacitor Capacitance must be at least 2 mf per 1 A load current good smoothing capacitance too less smoothing capacitance

24 Voltage stabilization

25 The simple stabilizer with a Zener diode This is the simplest and cheapest way, how stabilize output voltage. Today is unused to stabilize. Positives: Simple wiring Low price Negatives Large inside resistance Low effectivity Low output current Supply voltage must be 1,5~2 times bigger then output voltage

26 Circuit diagram Inside resistance of this stabilizer is about 10Ω. Low maximal output current [ma] Picture of a diodes V-A characteristic of Zener Diode

27 Stabilizers with fixed output voltage This way, how to stabilize output voltage is the most commonly. Stabilizers are produced as three outlets integrated circuit. Each types are produced in each packages. Table of packages of each stabilizers

28 Circuit diagram Type table of stabilizers with fixed output voltage (part1) Positive 78xx Positive 78xx xx maximal output current[a] package output voltage [V] xx maximal output current[a] package output voltage [V] 05 1,5 5 S05 2, ,5 6 S09 2, ,5 8 S12 2, ,5 12 S15 2, ,5 15 S18 2, ,5 24 S24 2,2 24

29 Type table of stabilizers with fixed output voltage (part2) Negative 79xx Positive 79xx xx maximal output current[a] -1,5-1,5-1,5 package output voltage [V] xx L05 L12 L15 maximal output current[a] -0,1-0,1-0,1 package TO-92 TO-92 TO-92 output voltage [V] , , ,5-24 All of this stabilizers are produced in SMD package positives: Large inside resistance Simple wiring Low price

30 Effect of bad stabilization

31 Stabilizers with adjustable output voltage By this type of stabilizer is possible to use to changing output voltage at intervals of 1.2VDC up to 37VDC. Output voltage and maximal current depends on each type. This stabilizers are produced in several packages (like, TO- 92, TO-3) TO-3 is used to higher output power. Type table of adjustable output voltage LM317(x) K T L LM337(x) T max.output current[a] 2,2 1,5 0,1 max. output current[a] -1,5 min. output voltage[v] 1,2 1,2 1,2 min. output voltage[v] -1,2 max. output voltage[v] max. output voltage[v] -37 package TO-3 TO-92 package

32 Power supply

33 Power supply

34 Power supply

35 Power supply

36 THE END