| 摘要 |
PROBLEM TO BE SOLVED: To provide a switching power supply that can suppress discharge current at the turn-on time to reduce a surge voltage occurring in a rectifying diode.SOLUTION: A switching power supply for applying an input voltage to a primary coil P of a transformer T so that a switching element Q1 connected to the primary coil P of the transformer T performs ON/OFF operation, thereby inducing a pulse voltage in a secondary coil S of the transformer T, and outputting an output voltage Vo obtained by rectifying and smoothing the pulse voltage with a secondary side rectifying circuit having a rectifying diode D1 and a smoothing capacitor C2, has a transient state detection circuit (a timer circuit 14, an overload detection circuit 15) for detecting an overload state and outputting a soft drive instruction signal, and a drive circuit 11 for making the switching element Q1 perform an on/off operation according to a soft drive operation in which the charging speed of a gate voltage during passage of the gate voltage over a gate threshold voltage is delayed as compared with a normal operation when the soft drive instruction signal is input. |
