Patent ID: 6269012
Filing Date: 2001-07-31
Classification: H02M,Y02B

Abstract:
A power supply unit comprising:a transformer having a primary winding connected to an AC commercial power supply;a bidirectional switch unit connected in series between the primary winding and the AC commercial power supply;an AC/DC converting circuit connected to a secondary winding of the transformer to deliver a DC output voltage: anda switch control circuit for intermittently controlling an ON/OFF operation of the bidirectional switch unit according to an output of the AC/DC converting circuit and a cycle of the AC commercial power supply, the switch control circuit including an output voltage feedback circuit which delivers a feedback signal when the DC output voltage is less than a predetermined value, a phase detecting circuit which detects a peak value of an AC commercial power supply input to output a peak detection signal and a latch circuit which latches the feedback signal and turns on the bidirectional switch unit in response to the peak detecting signal when the feedback signal is latched in the latch circuit;wherein the bidirectional switch unit is not turned on for a plurality of cycles of the AC commercial power supply input, when no feedback signal is latched in the latch circuit.