SWITCHING POWER SUPPLY DEVICE

摘要

PROBLEM TO BE SOLVED: To suppress a surge current at the time when a power transistor is turned ON.SOLUTION: A switching power supply device comprises: an inductor L0; a power transistor MP1 that performs switching of an input voltage by being turned ON and OFF; a rectifying and smoothing circuit that generates an output voltage from an AC voltage at an output side of the inductor L0; and a control circuit that ON/OFF-controls the power transistor MP1. The control circuit includes a drive circuit 10. The drive circuit 10 has: a power transistor OFF circuit 13 that turns OFF the power transistor MP1 when a voltage VOFF is valid; a level shift circuit 11 for shifting a level of a voltage VON that changes at an inclination depending on a level of the output voltage of the rectifying and smoothing circuit when the voltage VOFF is invalid; and a buffer circuit 12 that gradually makes the power transistor approach an ON state by an output of the level shift circuit 11, and then, turns ON the power transistor.SELECTED DRAWING: Figure 1