Patent ID: 6680854
Filing Date: 2004-01-20
Classification: H02M,Y02B,Y02P

Abstract:
A switching power supply capable of translating a.c. voltage into d.c. voltage, comprising:(a) a pair of a.c. input terminals for inputting a.c. voltage having a known frequency; (b) a pair of d.c. output terminals for outputting d.c. voltage; (c) a rectifier circuit connected to the pair of input terminals for rectifying the a.c. input voltage, the rectifier circuit having a first and a second output; (d) a transformer connected to the pair of a.c. input terminals via the rectifier circuit on one hand and, on the other hand, to the pair of d.c. output terminals, the transformer having a primary and an ancillary winding; (e) a rectifying and smoothing circuit connected between the transformer and the pair of d.c. output terminals for providing the d.c. output voltage; (f) a smoothing capacitor connected between a first extremity of the primary winding of the transformer and the second output of the rectifier circuit; (g) an inductor connected between the first output of the rectifier circuit and the smoothing capacitor via at least part of the primary winding of the transformer; (h) a primary switch connected between a second extremity of the primary winding of the transformer and the second output of the rectifier circuit; (i) soft-switching capacitance means associated with the primary switch; (j) an ancillary switch connected in parallel with the smoothing capacitor via at least the ancillary winding of the transformer for supplying to the ancillary winding a current of sufficient magnitude to cause the primary winding of the transformer to develop a voltage that enables the soft-switching capacitance means to discharge; and (k) a switch control circuit connected to the primary switch for on-off control of the primary switch at a repetition frequency higher than the frequency of the a.c. input voltage, the switch control circuit being also connected to the ancillary switch in order to initiate conduction through the ancillary switch earlier than the beginning of each conducting period of the primary switch and to terminate conduction through the ancillary switch not later than the end of each conducting period of the primary switch.