Community College of Allegheny County Unit 8 Page #1. Op-Amps

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1 Community College of Allegheny County Unit 8 Page #1 Op-s "You will say that I am always conjuring up awful difficulties & consequences my answer to this is it is an important part of the duty of an engineer" Robert Stephenson, the brains behind the Britannia Bridge, which opened in 1850 between Wales and the island of Anglesey. Quite a novel design, it stood for 120 years before being structurally compromised by a fire. Revised: Dan Wolf, 5/8/2018

2 Community College of Allegheny County Unit 8 Page #2 OBJECTIVES: Understanding of Op-s: a) lifier b) Non- lifier c) Comparator Circuit d) Adder e) Subtractor or Differential lifier Understanding the 741 Op- DELIVERABLES THAT YOU MUST SUBMIT 1. Table 1 (plus equations and comments) 2. Practice Problems On-Line Reading Material for Op-s: Required: a) Characteristics of Operational lifiers b) c) d) Optional: a) b) c) d) INTRODUCTION TO THE 741 OP-AMP: An Op- is a Voltage lifier which can be used in multiple configurations: a) lifier where the signal is both amplified and inverted.

3 Community College of Allegheny County Unit 8 Page #3 b) Non- lifier where the signal is amplified. c) Comparator Circuit which compares two voltages and then drives the output to one of two states, so essentially it is a one bit Analog to Digital convertor. d) Adder circuit which outputs the sum of two input voltages. e) Subtractor or Differential lifier which outputs the difference between two voltages. The key operating characteristics of an Op- are: 1) Open Loop Gain (Avo) is the gain of the op-amp without positive or negative feedback, typically it is about 20,000 to 200,000. 2) Input Impedance (Zin) is the ratio of input voltage to input current, assumed to be infinite but unavoidably, input leakage is about 80nA for the 741 due to a typical input impedance of 2M ohm. 3) Output Impedance (Zout) is assumed to be zero so that no internal resistance is in series with the load, typically it is about 75 ohms for the ) Bandwidth (BW) ideally it will amplify a signal from DC to very high AC. The upper limit for the 741 is about 100Khz. 5) Offset Voltage (Vio) the output voltage when both inputs are grounded, ideally = 0. This is typically 2 to 6mV for the ) Supply Voltage, the 741C can work with a supply voltage up to +/-18V. The 741 and 741A will work up to +/-22 Volts. EQUIPMENT REQUIRED: Op- IC 2. 10KΩ resister, Qty= KΩ resister 4. 10KΩ, 10-turn potentiometer 5. Signal Generator 6. +/-12V power supply 7. Oscilloscope

4 Community College of Allegheny County Unit 8 Page #4 Experiment #1 741 lifier: 1. Figure #1 shows a 741 Op- circuit for an inverting amplifier. Construct the circuit using a signal generator at the input and an oscilloscope to monitor the analog output voltage. Set the signal generator to generate a 0.5V PP AC signal. When complete, ask the instructor to review your setup before applying power. 2. Apply power and test the circuit. Complete the first half of Table #1 for this experiment and record your results. 3. Compute the equation for this data and include it along with Table #1. Is it linear? 4. Submit Table #1 as your documentation for this experiment. Table #1 Calculated Gain Input Voltage Output Voltage Measured Gain Non- Non- Non- 0.5V 1V 2V 0.1V 0.2V 0.3V

5 Community College of Allegheny County Unit 8 Page #5 Experiment #2 Non- 741 lifier: 1. Figure #2 shows a 741 Op- circuit for a non-inverting amplifier. Construct the circuit using a signal generator at the input and an oscilloscope to monitor the analog output voltage. Set the signal generator to generate a 0.1V PP AC signal. When complete, ask the instructor to review your setup before applying power. 2. Apply power and test the circuit. Complete the second half of Table #1 for this experiment and record your results. 3. Compute the equation for this data and include it along with Table #1. Is it linear? 4. Submit Table #1 as your documentation for this experiment.

6 Community College of Allegheny County Unit 8 Page #6 Figure #1 741 lifier Gain (AV) = Rf R1 Vout = Vin * AV R2 adjusts the offset Figure #2 741 Non- lifier +12V Vin V 6 Vout Gain (AV) = Vout Vin or Gain (AV) = 1+ Rf Rin Vout = Vin * AV Rin = 10K Rf = 47K

7 Community College of Allegheny County Unit 8 Page #7 PRACTICE PROBLEMS: 1. If we apply 10mV to the input of Figure #2, what will the output be? 2. What resister values would you use to get a gain of 15 for the inverting Op- as shown in Figure #1? 3. Refer to the 741 Datasheet that is located on the course website and which describes three different versions of the 741. Note: Datasheets are not all equal so attach a copy of the datasheet that you used. a. What is the maximum supply voltage for the LM741C Op-? b. What is the maximum input offset voltage for the C version of the 741 Op- (LM741C)? c. What is minimum bandwidth for the LM741A Op-? d. We have been asked to design an application for a steel manufacturer which will be required to operate at temperatures up to 180 F. Should we use the LM741, LM741A or LM741C version of the Op-?