Patent ID: 8027176
Filing Date: 2011-09-27
Classification: H02M,Y02B

Abstract:
1. A switching power supply circuit, comprising: a first switching element which has a fly-back transformer with a magnetizing coil and a drive coil at the primary side and an output coil at the secondary side and a bipolar transistor applying a voltage from said drive coil for self-oscillation and then magnetizing said magnetizing coil, a second switching element with a bipolar transistor to control the switching time of the first switching element, a timing condenser connected between the base and emitter of the second switching element, and supplying the current from said drive coil through an impedance circuit in order to supply the direct-current voltage that is rectified from AC voltage to said magnetizing coil and outputting the voltage from said output coil by switching, and a sensing coil being connected magnetically closely with said output coil and being connected with a rectifying and smoothing circuit, the rectifying and smoothing circuit being connected with said timing condenser through a Zener diode facing in the inverse direction to the resistance, and the discharge and charge property of said timing condenser being adjusted by resistances connected in series with said Zener diode in order to make the timing for said second switching element to turn on at the non-loading time shorter than that at the ordinary switching time.