Switching type AC adapter circuit with a latch protection circuit

摘要

Disposed in a secondary side circuit and is connected to a constant voltage control circuit (22), to an overcurrent detection circuit (24), and to an overvoltage detection circuit (26), a photocoupler control circuit (28) controls a photocoupler (IC1) so as to feed a constant voltage detection control signal as a feedback signal back to a primary side circuit. The photocoupler control circuit (28) controls the photocoupler (IC1) so as to turn it off when the photocoupler control circuit is supplied with at least one of an overcurrent detected signal and an overvoltage detected signal. A voltage detection circuit (18) makes a latch circuit (16) operate when the voltage detection circuit detects a voltage induced in an auxiliary winding (NSLD) of a transformer with the photocoupler turned off, thereby making a switching operation of a switching type AC adapter circuit stop.