That's pretty much it. The secondary windings are actually all doubled in the number of turns. Otherwise I'd need 1.5 turns on the primary. Talk about a peak current! The output cross regulation is within 5%, so doubling the windings didn't droop the output.
Originally posted by magnetik:
So what does the transformer windings do? raise the input voltage higher??? like an inverter???? or am I missing something.???
Basically what a ATX AC-DC power supply does is takes the 120 in, converts it to 170 with a bridge rectifier and caps. It is then switched on off into the primary of a high frequency transformer. The secondarys have a turn ratio with the primary such that 170 goes to 12, 5, 3.3 etc..
If I'm not mistaken, and correct me if I'm wrong, all that Presslab did was rewind the transformer so that the secondary windings look the same as they did before but the primary has a lot less turns so that an input of 12 volts can be used instead of the 170 volts. He scrapped the old transformer because the current on the primary previously was fairly low at 170 volts but now to get the same kind of power rating, he needed a lot more current and the old transformer would saturate (cause problems under heavy load). He scrapped the pwm circuit for controlling the 170 volt transistor switcher and used his own for the new 12 volt one. Is that more or less it?