Design of performance tester based on operational amplifier

By utilizing the comparative characteristic design of the operational amplifier input, an operational amplifier fast tester is made, which can quickly and accurately determine the quality of the operational amplifier being tested, and is very useful in component selection.

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] R3R4Rp to form a V- voltage bias circuit, and Rp is adjusted downward, but V-V+, Vd2 emits light. Resistors R5R6C1C2 form a power splitting circuit, which divides the 9V power supply into 2*4.5V, so that 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 to meet the test of general single, dual, and quad operational amplifiers. The principle of the tester is shown in the figure below.

Tester debugging

The tester has two eight-pin and one fourteen-pin integrated circuit DIP sockets, combined with light-emitting diodes and power supplies. Socket 1 is used to measure a single op amp, 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 a dual op amp, 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 a quad op amp, with pin 4 as the positive power supply, pin 11 as the negative power supply, pins 2, 6, 9, and 13 input negative, pins 3, 5, 10, and 12 input positive, and pins 1, 7, 8, and 14 output. IC1, IC2, and IC3 in the circuit diagram 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 to ensure that they are virtual grounds. R5 and R6 can be selected between 200 and 510 ohms because they are power fission resistors and current limiting resistors of light-emitting diodes. Small resistance, bright light, high power consumption. Large resistance, weak light, difficult to observe. R1, R2, R3, R4 should be as equal as possible to ensure that the bias is "ground". Select a linear potentiometer with Rp of the same order of magnitude between 10k-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, and pay attention to the position of the pins. Then close K to adjust Rp and observe, and judge whether it is good or bad according to the state of the light-emitting tube. After the test, turn off the power and remove the integrated circuit. Note that the integrated circuit cannot be plugged in or unplugged with power on to avoid damage to the integrated circuit.

How to use the 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, Vd1 and Vd2 will light up. When testing the dual op amp, insert the dual op amp (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 the quad op amp (IC1, IC2, IC3, IC3), insert the op amp under test into the socket DIP3, adjust Rp downward, Vd1, Vd3, Vd5 and Vd7 will light up; adjust Rp upward, Vd2, Vd4, Vd6 and 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 to observe the brightness of the LED and the difference in the time between on and off to judge the consistency of the multi-op amps. If there is only one state when adjusting RP during the test without change, it means that the op amp has lost its comparison characteristics and is damaged and cannot be used.