To restrain a reverse flow during parallel operation of switching power supply units, capable of carrying out a stabilized parallel operation.
This switching power supply unit including a synchronous rectifying circuit supplies stabilized DC power to a load R through the synchronous rectifying circuit. The synchronous rectifying circuit permits a control circuit CONT to turn on/off a switching transistor Q1 connected to a primary winding N1 of a transformer T, and turns on/off an electric field-effect transistor Q2 complementarily to the switching transistor Q1 by applying the induced voltage on a tertiary winding N3 to the gate of the electric field effect transistor Q2 for rectifying the induced voltage of a secondary winding N2, and outputs DC voltage through a filter capacitor C0. This switching power supply unit is also provided with a time constant circuit consisting of a resistor R1 and a capacitor C1 applying the induced voltage on the tertiary winding N3 of the transformer T, and a transistor Q3 which applies the terminal voltage of the capacitor C1 of the time constant circuit to the gate and is turned on to short the input capacity Ci of the electric field-effect transistor Q2 for rectification when the terminal voltage exceeds a threshold.
AOKI ISAMU
KOBAYASHI KAZUO
NISHIMURA KATSUHIKO
Next Patent: SYNCHRONOUS RECTIFYING CIRCUIT FOR SWITCHING POWER SUPPLY