DIY Production of Operational Amplifier Tester

　　By using the comparative characteristics of the operational amplifier input, the operational amplifier tester can quickly and accurately determine the quality of the measured operational amplifier, which is very useful in the selection of components. The author used this small instrument to select the purchased operational amplifiers (including some disassembled products) in the process of guiding students in practical training, and the effect was very good.

　　Circuit Principle

　　The basic design idea of ​​the tester is to connect the operational amplifier to be tested (IC1, IC2, IC3, IC4 in the figure) into a comparator structure. When V+ > V-, Vout is in the positive power state. Close to Vcc, the light-emitting diode Vd1 emits light. When V+ < V-, it is in the negative power state, close to Vee, and the light-emitting diode Vd2 is bright. For this reason, R1 and R2 are used to set V+ = 1/2 (Vcc-Vee} = 0 [for the potential of point E], and R3, R4, and Rp form a V- voltage bias circuit. Adjust Rp downward, but V- < V+. Vdl emits light; adjust RP upward. V- > V+. Vd2 emits light. Resistors R5, R6, C1, and C2 form a power splitting circuit. The 9V power supply is divided into 2*4.5V. Make Ve=0v, that is, Vdd=+4.5v, Vee=-4.5v, which meets the requirements of dual power supply applications of operational amplifiers.

　　In the circuit, R7-R14 are input series resistors. The purpose is to prevent the damage of the input of one operational amplifier from affecting the test of other operational amplifiers when testing multiple operational amplifiers. Two 8-pin and one 14-pin DIP sockets are used in the circuit design. This satisfies the test of general single, dual, and quad operational amplifiers. The principle of the tester is shown in the figure below.

　　Debugging of Op Amp Tester

　　The tester has two 8-pin and one 14-pin integrated circuit DIP sockets, combined with light-emitting diodes and power supplies. Socket 1 is used to measure single op amps, with pin 7 connected to the positive power supply, pin 4 connected to the negative power supply, pin 2 input negative, pin 3 input positive, and pin 6 output. Socket 2 measures dual op amps, with pin 8 as the positive power supply, pin 4 as the negative power supply, pins 2 and 6 input negative, pins 3 and 5 input positive, and pins 1 and 7 output. Socket 3 measures quad op amps, with pin 4 as the positive power supply, pin 11 as the negative power supply, pins 2, 6, 9, 13 input negative, pins 3, 5, 10, 12 input positive, and pins 1, 7, 8, 14 output. In the circuit diagram, IC1, IC2, and IC3 are given as a principle explanation. In fact, the wiring of sockets 1, 2, and 3 should be connected as above. As long as the wiring is correct, there is almost no need for debugging. R5 and R6 should be as equal as possible. Make sure they are virtual grounds. R5 and R6 are power fission resistors and current limiting resistors of light-emitting diodes. It can be selected between 200 and 510 ohms. Small resistance, bright light, high power consumption. Large resistance, weak light, difficult to observe. R1, R2, R3, R4 should be as equal as possible. Ensure that the bias is "ground". Select a linear potentiometer with Rp of the same order of magnitude between 10k and 100k, and make a scale line in the middle for adjustment. (The values ​​of the resistors marked on the circuit diagram are for reference only. When making, you can choose according to the resistors you have on hand) VD1-VD8 select different-color light-emitting diodes for easy distinction. Turn off the power before measuring, insert the integrated circuit to be tested, single op amp, dual op amp, and quad op amp into the corresponding sockets respectively, pay attention to the pin position can not be inserted in reverse, then close K to adjust Rp to observe, judge whether it is good or bad according to the state of the light-emitting tube, turn off the power after the test, and remove the integrated circuit. Note that the integrated circuit cannot be plugged in and out with power on to avoid damage to the integrated circuit.

　　How to use the op amp tester

　　Insert the single op amp (IC1) under test into the socket DIP1, turn on the power, adjust Rp downward, Vd1 will light up; adjust Rp upward, Vd2 will light up, when RP is in the middle position. The output is zero, and Vd1 and Vd2 will light up. When testing dual op amps, insert the dual op amps (IC1, IC2) under test into the socket DIP2, adjust Rp downward, Vd1 and Vd3 will light up. Adjust Rp upward, Vd2 and Vd4 will light up; when testing quad op amps (IC1, IC2, IC3, IC3). Insert the op amp under test into the socket DIP3, adjust Rp downward, Vd1, Vd3, Vd5, Vd7 will light up; adjust Rp upward, Vd2, Vd4, Vd6, Vd8 will light up. There is no need to find the midpoint during the test, as long as the changing state of the light-emitting tube is observed, the quality of its comparative characteristics can be judged. For the test of multiple op amps. Rp should be adjusted slowly. In order to observe the brightness of the light-emitting diode and the difference in the time of on and off to judge the consistency characteristics of its multi-op amp. If there is only one state when adjusting RP during the test, and it does not change, it means that the op amp has lost its comparison characteristics and is damaged and cannot be used.

　　summary

　　I used this small instrument to test single op amp LM741, CA3140, CA3130, NE5534, dual op amp LM358, MC1458, TL062, TL082, quad op amp LM324, TL084, LM747. The results are ideal. It is very useful for screening disassembled components.