Power Supply – Limiting Short Circuit Current

currentpowerpower supplyresistorsshort-circuit

I'm using a repurposed ATX power supply for my hobby projects since it's got 3.3/±5/±12 outputs, all of which are really convenient. But one thing I didn't really think about until I slipped my probes across the pins of an opamp, since I've always dealt with commercial/proper lab power supplies in my school labs, was that an ATX power supply will gladly deliver lots of current if that 12V line (or any other) is shorted to ground. The poor LM318 didn't stand a chance. My meter and supply survived, but in the interest of not killing anything in the future, myself included, I was wondering what the best option was for short/overcurrent protection?

I was thinking of sticking some high wattage resistors at the output of the supply before connecting them to the rails of my project breadboard (I use a separate breadboard with terminal blocks for power, which the ATX supply connects to). The problem is if I'm drawing a lot of current (LEDs etc) this will sag the voltage on the line. And, for example, if I use a 1W 200ohm resistor on the 12V line, it limits my current to only 60mA – if I want more, I need some really beefy wattage resistors. I can probably work around the voltage sagging by using a voltage regulator (eg at 10V), but this all doesn't seem like the best way to go about doing things.

I'd appreciate some input from someone more experienced than I am.

Best Answer

Use a fuse. You can buy e.g. PTC resettable fuses that will limit the high current and will automatically reset after some time.