Help about ATX power supply

Dodgydave

Joined Jun 22, 2012
11,284
Your 3.3v line is regulated by the Tl431 zener, when it reaches 3.5v, it conducts and turns on Q5 which pulls the supply down by making it more Negative using the diodes D28/29, the inductors T1403, are for filtering the supply out, when the supply drops to 3V the Tl431 turns off and the cycle repeats.
 
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