| 摘要 |
PROBLEM TO BE SOLVED: To configure an isolated switching power supply having a combined transformer and a protective function.SOLUTION: Under normal operating conditions, the divided voltage of resistors R6, R7 is higher than a reference voltage Vref. Accordingly, the output voltage of a comparator CMP2 is at the L level. A multi-vibrator MV3 oscillates and a state in which a pulse signal is transmitted through a second signal transmission transformer T3 is continued. As a result, the output voltage of a hiccup control circuit 53 is kept at the L level and does not interfere with the oscillation operation of the multi-vibrator MV1. Thus the switching operation of a power switch Q1 is continued. When an overcurrent protection circuit 59 is actuated, the generation timing of a pulse signal transmitted at a first signal transmission transformer T2 is advanced and the on duty of the power switch Q1 is reduced. As a result, the output voltage droops and the divided voltage of the resistors R6, R7 lowers. The oscillation of the multi-vibrator MV3 is stopped and a pulse signal is not output any more. |
