simple opamp tester

This circuit is similar in principle to, and can be mounted in the same box as, the 555 tester described elsewhere in this issue. The opamp to be tested is connected as a simple square-wave oscillator. When pushbutton S1 is closed, the non-inverting input of the opamp is held at a reference voltage derived from the output voltage and the potential divider R2/R3. The current through R1 is used to charge capacitor C1 until the voltage level on the inverting input reaches that of the reference voltage. Since the opamp acts as a comparator, its output level will change state thereby producing a reference voltage of opposite polarity. The charge current for C1 will then flow in the opposite direction until the new reference voltage is reached and the whole cycle will be repeated. When the output is high, transistor T1 will conduct and LED D1 will be Sla 9 simple opamp tester C1 R3 mim in on. Conversely, when the output is low T2 will conduct and LED D2 will be on. The transistors are i...