UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post

SiriusHardware · 22nd Nov 2022, 12:17 pm

+1 for not using this method to run up anything with a switch-mode power supply in it: As has been stated they will try to maintain their output into the output load by drawing as much extra input current as they need to, to compensate for the lack of input volts.

If the input voltage is really low then the current drawn is almost certain to exceed the maximum input current that the PSU was designed for.

It is why so many devices expire during a mains power brown-out where the lights fade right down for a second or so. Some SMPSUs do have low input voltage detection and will shut off if the input is excessively low, many older ones do not.

22nd Nov 2022, 12:17 pm	#6
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,586	Re: Using a variac when testing always wise? +1 for not using this method to run up anything with a switch-mode power supply in it: As has been stated they will try to maintain their output into the output load by drawing as much extra input current as they need to, to compensate for the lack of input volts. If the input voltage is really low then the current drawn is almost certain to exceed the maximum input current that the PSU was designed for. It is why so many devices expire during a mains power brown-out where the lights fade right down for a second or so. Some SMPSUs do have low input voltage detection and will shut off if the input is excessively low, many older ones do not.