What does one do when designing a power supply? Well, build a power supply tester, of course. One of the simplest things to build is a constant current load. This will allow for testing of the endurance of the power supply, as most of the designs out there are using slow components.
However, I wanted to make a better one: one that I could hook up to my Analog Discovery and generate a test waveform to be able to connect and disconnect the load fast. This is a weekend project, so all parts are not the best for the purpose, just what I had around.
Warning: The analog discovery is grounded through your PC (unless using a laptop on battery only) so you have to make sure that both the supply being tested and the auxiliary 12V supply are isolated and not grounded. Or use an isolated aux supply and a USB optical isolator if the supply under test is grounded.
The simplest of design, one OP-AMP driving 3 MOSFETs. All fine until I made a mistake: with the signal generator connected and turned ON, i connected a 24V 5A supply that was already on, while the signal generator was providing a square wave for 5A current. This caused one of the MOSFETs to blow up (shorting) due to an avalanche event. Finally the power supply went into hiccup mode.
fore more detail: PSU Burner