Patent ID: 8243473
Filing Date: 2012-08-14
Classification: H02M,Y02B

Abstract:
1. A switching power supply device, in which an input DC voltage is applied to a series resonance circuit, and a prescribed output voltage is generated via a transformer and power is supplied to a load, comprising: a series resonance circuit, having a current resonance inductor and a current resonance capacitor; a plurality of main switching elements or main switching element groups, which are turned on and off in alternation to switch a current path of the series resonance circuit; a transformer, which causes a secondary-side current to be induced from the series resonance circuit by primary-side on/off control of the main switching elements or main switching element groups; a plurality of diode rectifying elements, which are turned on and off corresponding to the plurality of main switching elements or main switching element groups, to rectify the secondary current of the transformer; and a load judgment circuit, which generates a reference time signal having a prescribed time width, with a turn-on timing of the main switching elements or main switching element groups as a starting point; wherein a light loading state of the load is judged by comparing a delay time of a conduction timing of the diode rectifying elements from the turn-on timing of the main switching elements or main switching element groups corresponding to the diode rectifying elements with the reference time signal generated by the load judgment circuit; and the switching power supply device further comprising: a light load judgment circuit, which generates an alarm signal when the delay time of the conduction timing of the diode rectifying elements exceeds the time width of the reference time signal generated by the load judgment circuit.