| 摘要 |
PROBLEM TO BE SOLVED: To provide a switching power supply device capable of setting a timing when a power transistor is turned on to a bottom of free vibration, with a simple circuit configuration.SOLUTION: A switching power supply device comprises: a voltage/current conversion circuit 10; a voltage clamp circuit 20; a capacitor C3 charged and discharged by the voltage clamp circuit 20; a capacitor C4 charged by the clamp circuit 20 via a resistor R1 independently of the capacitor C3, and discharged via the resistor R1; a timing current generation circuit 50 that charges the capacitor C4 via the resistor R1 with a current that is larger as an output voltage of a rectifying and smoothing circuit is lower; and a drive circuit 30 that, when a voltage charged in the capacitor C3 becomes larger than a voltage V1, turns off a power transistor MP1 and discharges the capacitor C4, and when a voltage of the capacitor C4 and a composite voltage generated at the resistor R1 become larger than a voltage V2, turns on the power transistor MP1.SELECTED DRAWING: Figure 3 |
