Computer PSU start circuit with bicolor LED

There are a lot of tutorials on the internet on how to turn a computer PSU into a bench top power supply. Most of them involve adding a load on the 5V line and turning the PSU on by grounding the PS_ON wire via a switch. Here is a nice indicator and turn on/off switch for computer PSUs.

ATX PSUs work well under rather constant loads. So if you power up the PSU with a small load of a few tens miliamps and then connect a greater load, for example a car light bulb which may require 3-4 A, the PSU may shut down. The same happens in case of an accidental shortcircuit. You may believe that the PSU got broken or its fuse got blown. That's not true. The PSU automatically shut itself off.

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