Patent ID: 7394670
Filing Date: 2008-07-01
Classification: H02M

Abstract:
1. A switching power source comprising a DC power supply; a transformer having primary and secondary windings; a switching element connected to the DC power supply through the primary winding of the transformer; a rectifying smoother connected to the secondary winding of the transformer to produce a DC output voltage; and a control circuit for producing drive signals to the switching element to turn the switching element on and off in order to keep the DC output voltage substantially constant, said control circuit comprising a voltage detector for detecting a voltage of the DC power supply to produce a detection voltage; a comparator for producing an output signal when the detection voltage from the voltage detector exceeds a reference voltage; a bottom voltage detector for detecting a bottom point in the voltage across the switching element after energy has been discharged from the transformer; and a switching controller for selectively turning the switching element on depending on existence or absence of the output signal from the comparator.