Discussion in 'Homebrew and Kit Projects' started by KD9KSO, Apr 15, 2018 at 5:38 PM.
No, but I was half expecting it. I ran it for a couple of hours with no load and it stayed on.
I've done a few of those PC power supply projects. The ones that are easiest to modify to use are the ATX models from a few years back. They have a TL494 IC that does the regulation, by employing reference voltages comparisons with the +5VDC or a combination of +5VDC and +12VDC. On the one I use for the base station 40W 2m FM transceiver, I adjusted it for +13.6VDC out. All that is required is to change a resistor on the board that is part of a voltage divider in the feedback circuit to Pin 1, and in my case, removing the feedback line from monitoring the +5VDC output (removed another resistor.) The Voltage at Pin 1 is compared with the 2.5V reference at Pin 2.
I remove extraneous 5V wiring and I re-mount the fan outside the case. I put a 10-ohm 10W resistor in the circuit so that there is a load on the +5V line so that the power supply will start with a load
There a dozens of articles and schematics on the web. AC8GY has a mod that explains the voltage divider and comparator circuit. Also, search on "Seventeam PC power supply conversion" for a typical schematic that shows the subcircuit for regulation. Your supply will have similar components if it uses the TL494 chip. Tracing the circuit in the feedback line(s) from the +12VDC is pretty easy. Here is
what it looks like on my supply.
Good info thanks, I may have a go at mine now.
Looks like you have bypassed the mains, common mode choke though?
Thanks for the info!