I had a hair-brained idea the other day and put together the attached circuit.
The problem: the instant I push the switch to place a voltage across the inductor, the power supply shuts down. Clearly this is some sort of emergency power-down because I can start it right back up, but I'm not understanding why such a feature would get triggered? Is it just the voltage drop is sudden enough to flip off such a power supply? I would have thought that the series resistance would be enough to prevent something like this.
simulate this circuit – Schematic created using CircuitLab
Best Answer
The above circuit in of itself would not cause the 5V ATX supply to drop out, as the max amount of power that this circuit could draw would be ~12mA. The circuit may have been built something a little different than the one listed above and may be shorting out, test it with a benchtop supply before using it on an ATX supply.
The ATX power supply probably has overcurrent, and/or undervoltage protection. Undervoltage protection is the most likely, if the supply dips below a given voltage (say 4.7V) for an extended amount of time, the supply shuts down.
If you're looking to dim the LED slowly and turn it on slowly, a mosfet with an RC for the input might be best.
Like this: