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Unformatted text preview: L AB 8: O PERATIONAL A MPLIFIER C IRCUITS- E LECTRONIC M ANOMETER I Objective and background: The goal of this laboratory is to help you review basic operational amplifier circuits where the op- amp is used open-loop (no feedback resistor) or closed-loop (with a feedback resistor). The objectives of the laboratory are: 1. To measure the saturation voltages of a 741 op-amp; 2. To analyze, build and demonstrate the function of a positive level dectector; 3. To analyze, build and test a noninverting op-amp amplifier and an inverting op-amp amplifier; 4. To diagnose certain faults in op-amp amplifier circuits 5. To combine a single op-amp differential amplifier and a pressure transducer to build a simple electronic manometer. A 741 operational amplifier chip and the op-amp symbol are represented on the following graph. The op- amp is a high-gain differential amplifier with two inputs: the noninverting input Vin+ (pin 3) and the inverting input Vin- (pin 2). The op-amp has one output Vout (pin 6). In open loop circuits, the output voltage Vout is related to the difference (Vin+ - Vin-): Vout = A (Vin + - Vin-) ol The open-loop gain A ol is very large: 100,000 or more. Therefore the slightest difference between the two input voltages brings the op-amp into saturation. The output voltage is one of the saturation voltages (+V sat ) or (-V sat ). The saturation voltages are related to the supply voltages V CC and -V CC at pins 7 and 4: +Vsat V- 2 volts-Vsat - V + 2 volts CC CC 4-Vcc V in+ 3 5 6 V in- 2 1 7 8 V in+ Vou t-Vcc V in- +Vc c +Vc c Vou t Many useful op-amp amplifiers circuits use negative feedback materialized by a resistor between the output of the operational amplifier and the inverting input. Circuits with negative feedback have a closed- loop gain that does not depend on the open-loop gain. The closed-loop gain is function of external resistors 1 attached to the op-amp pins. Op-amp circuits with negative feedback are analyzed using the following rules: 1. The voltages at the input pins are equal: Vin+ = Vin-; 2. The inputs do not draw or source any current: I in + = I in- = 0. II Saturation voltages: Prelab: Consider a 741 op-amp used "open-loop" and powered with a +15/-15 V split supply. V in+ V in- Vou t +15 V-15 V Use the information provided in the "background" section to predict the output voltage Vout for the following conditions (if the output cannot be predicted, enter a ?): Vin+ 0.1 V 1 V-1 V 0 V 0 V 0 V 1 V 0.3 V-5 V Vin- 0 V 0 V 0 V 1 V- 1 V 0 V 1 V 0.4 V-2 V Vout 13 13-13-13 13 ? ?-13-13 Procedures: a) Connect a 741 op-amp as shown on the following diagram. b) Set up the input voltage conditions listed in table 1 below by selecting the proper power source for the potentiometers and adjusting the wiper positions; Use the scope to read the two input voltages and the DMM to read the output voltage Vout for the following conditions. Compare with the predictions from the prelab....
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- Spring '08