Summary of PSU Burner
This article describes a weekend project to build an advanced constant current load tester for power supplies, enabling fast connect/disconnect testing via an Analog Discovery signal generator. The author details a design using one op-amp driving three MOSFETs but shares a cautionary tale about an avalanche event that blew up a MOSFET when connecting a live 24V supply while the signal generator was active.
Parts used in the Constant Current Load Tester:
- Analog Discovery
- Signal Generator
- Op-Amp
- Three MOSFETs
- Auxiliary 12V Supply
- USB Optical Isolator (optional)
Intro
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
- What is the primary purpose of this project?
To test the endurance of power supplies by generating test waveforms to connect and disconnect the load fast. - Can I use any power supply for the auxiliary 12V source?
No, you must ensure it is isolated if the supply under test is grounded, or use an isolated aux supply. - Does the Analog Discovery require special grounding precautions?
Yes, it is grounded through your PC unless on battery, requiring isolation between the tested supply and the aux supply. - What caused the MOSFET to blow up in the author's experience?
An avalanche event occurred when connecting a live 24V supply while the signal generator was providing a square wave. - How many MOSFETs are driven by the single op-amp in this design?
The design uses one op-amp to drive three MOSFETs. - What tool did the author use to generate the test waveform?
The author used the Analog Discovery connected to a signal generator. - Is this project considered a high-end build with premium parts?
No, it is described as a weekend project using whatever parts were available rather than the best components. - What safety measure can prevent ground loop issues?
You can use a USB optical isolator if the supply under test is grounded.
