Patent ID: 7042739
Filing Date: 2006-05-09
Classification: H02M,Y02B

Abstract:
1. A switching electric source device comprising: a transformer including a primary winding, a secondary winding and a third winding; a main switching element connected to the primary winding of the transformer; a secondary rectifying smoothing circuit for rectifying and smoothing electric power output from the secondary winding of the transformer based on a switch on-off operation of the main switching element, and externally outputting the rectified, smoothed electric power; a detection circuit for indirectly detecting the output voltage from the secondary rectifying smoothing circuit utilizing voltage induced in the third winding of the transformer; and a control circuit for controlling the switch on-off operation of the main switching element for stabilization of the output voltage from the secondary rectifying smoothing circuit based on the detection voltage for the output voltage obtained by the detection circuit; wherein the secondary rectifying smoothing circuit includes a first synchronous rectifier connected in series with the secondary winding and arranged to perform the same switch on-off operation as that of the main switching element, and a second synchronous rectifier connected in parallel to the secondary winding and arranged to perform a switch on-off operation inverting that of the main switching element, the first and second synchronous rectifiers being operative to rectify the output power from the secondary winding, and a first synchronous rectifier control circuit is provided, which detects the resonance state generated based on the exciting energy of the primary winding after the main switching element switches off, and causes the first synchronous rectifier to switch on earlier during the time period from the completion of the resonance state to the switching on of the main switching element, based on the detection signal for the resonance state.