Patent ID: 6188207
Filing Date: 2001-02-13
Classification: H02M,Y02B

Abstract:
A switching power supply, comprising:a choke coil being in series at one of a pair of source supply lines to which a DC input voltage is supplied;a switching element connected between said pair of source supply lines, said switching element intermittently cutting off said DC input voltage applied to said choke coil; anda rectifier/smoothing circuit being input with a voltage achieved by superimposing a flyback voltage onto said DC input voltage, said flyback voltage being generated at said choke coil while said switching element is set in an OFF state, said rectifier/smoothing circuit including:a synchronous rectifying device constituted of an NPN transistor;a smoothing capacitor having a first end and a second end, said smoothing capacitor outputting a stepped up DC voltage at said first end and said second end, said first end being connected to said synchronous rectifying device; anda base drive circuit including:an auxiliary winding magnetically coupled with said choke coil;a DC blocking capacitor provided between said auxiliary winding and a base of said NPN transistor; anda reset circuit connected between said base of said NPN transistor and any one of said first end and said second end of said smoothing capacitor.