How to test an op-amp

In this article, I’ll show you quickly and simply how to test an op-amp.

To test a resistor you can just use a multimeter, set it to ohms and measure it. The resistor is working, simple.

Unfortunately, you can’t do this with an op-amp. A resistor is a simple passive component whereas an op-amp is a complex circuit made up of many components. For a start, it needs power connected to it to work at all.

For testing electronic components the easy way read my guide.

There are various ways you can test an op-amp. Each way has its advantages and disadvantages.

How to test an op-amp

Know your ins and outs

The first thing you need to know when testing an op amp is the pin out of the device you want to test. There are lots of different pin-outs for op amps. Some are single some are dual and some are quad. They all have different connections. The connections you need to know are the positive and negative power connections to the IC, the output and which are the inverting and non-inverting inputs.

Testing an op amp on a breadboard

This is just about the simplest way to test an op amp. You will need a breadboard and a power supply and a multimeter. I’ve set the power supply to provide 12V in this example but if you check the datasheet you’ll see that most op amps can be powered by quite a wide voltage range.

Connect the inverting input the output.

The way the circuit is configured is what is called a voltage follower. Connect the output of the op amp to the multi-meter and connect the input to 0V. The multimeter should read 0V. Don’t worry if it doesn’t read exactly 0V it should be low though. Disconnect the input to 0V and connect it to the positive supply. The multi-meter should read around 12V.

Testing with an oscilloscope

This is my favourite way of testing an op amp.

You connect up the same circuit as above but substitute the multi-meter with an oscilloscope. Instead of connecting the input of the op amp to 0V and 12V, I use a signal generator.

I set up to generate a square wave. You should then see this square wave at the output of the op amp as it’s just acting as a non-amplifying buffer.

If you disconnect the supply to the op amp the signal should disappear.

I like this way because it gives the op amp a test of putting a proper signal through it and you can clearly see the results.

Building an op amp tester

You can of course take the breadboard circuit and make it permanent on one of the breadboard circuit boards that you can solder on. If you test op amps a lot it will certainly save you time as you won’t have to build the breadboard circuit up every time you want to do a test.

You could also just use a circuit to make it a multi-vibrator and put a LED on it then you wouldn’t need to use any other test equipment.

The disadvantage of building a permanent circuit is that there are loads of different op amps, duals, and quads, all with different pinouts and if you use a socket you can only plug one type in. You could of course connect up lots of different IC sockets wired to the same test circuit.

Testing an op amp in the circuit

This is probably the most difficult method as you need more knowledge than the other described ways. You will need to know what the op amp is doing in the circuit. If you have read my post How to use an op amp, you will see that an op amp can be used in quite a few ways. An amplifier, an inverting amplifier or a comparator are just a few of the ways it could be configured.

If the device was being used as an amplifier you could connect up signal generator to the input and put an oscilloscope on the output and check the gain of the output signal was correct.

The advantages of this method are that you don’t have to disconnect the device and it’s already connected to power rails and ready to go.

The disadvantages are that you need a bit of experience in electronics to know what it’s supposed to be happening in the circuit. You also need an oscilloscope and something like a signal generator to connect the input to. The results can sometimes be a bit inconclusive which is the last thing you want from a test.

This method is best left for people with previous experience.