Switching power supply circuit

摘要

A switching power supply device includes: a main transformer; a main switch that is connected between a high potential terminal of an input direct current voltage source and a primary-side main winding; a synchronous rectifier circuit includes: a rectifying switch that is connected to a secondary-side main winding in series and that is turned ON in synchronization with a turning ON state of the main switch and a commutation switch that is connected to the rectifying switch series circuit in parallel and that is turned ON in synchronization with a turning OFF state of the main switch; and an auxiliary switch circuit that turns the commutation switch OFF. When the main switch stops a switching operation while a voltage exists at a first output terminal on a high potential side, the auxiliary switch circuit turns the commutation switch OFF to prevent continuation of self-excited oscillation.

主权项

1. A switching power supply device, comprising:
a main transformer that has a primary-side main winding and a secondary-side main winding; a main switch that is connected between a high potential terminal of an input direct current voltage source and the primary-side main winding; a synchronous rectifier circuit including:
a rectifying switch that is connected to the secondary-side main winding in series to form a rectifying switch series circuit and that is turned ON in synchronization with a turning ON state of the main switch; anda commutation switch that is connected to the rectifying switch series circuit in parallel and that is turned ON in synchronization with a turning OFF state of the main switch; and an auxiliary switch circuit that turns the commutation switch OFF, wherein when the main switch stops a switching operation while a voltage exists at a first output terminal on a high potential side, the auxiliary switch circuit is configured to turn the commutation switch OFF, the auxillary switch circuit includes:
a first rectifying device having a first cathode and a first anode, the first cathode being connected to a drain of the commutation switch, the first anode being connected to a second output terminal on a low potential side via a capacitor;a second rectifying device having a second cathode and a second anode, the second anode being connected to a control terminal of the commutation switch;a PNP bipolar transistor having:
a base connected to a node connected between the first rectifying device and the capacitor via a first resistor;a collector connected to a source of the commutation switch; andan emitter connected to the first output terminal on the high potential side via a second resistor; andan NPN bipolar transistor having:
a base connected to the emitter of the PNP bipolar transistor;a collector connected to the second cathode of the second rectifying device; andan emitter connected to the second output terminal on the low potential side, wherein the capacitor is connected between the base and the emitter.