Patent ID: 7035119

Claim:
A switching power source comprising a DC power source; a primary winding of a transformer and a switching element connected in series to the DC power source; a current detector for acquiring electric current flowing through the primary winding of the transformer or the switching element; a rectifying smoother connected to a secondary winding of the transformer for generating DC output voltage; and a control circuit for supplying the switching element with drive signals to turn the switching element on and off so as to keep the DC output voltage in a substantially constant level; said control circuit comprising a current comparator for comparing a voltage level of signals acquired by the current detector with a reference voltage level to produce detection signals of first or second level; an edge detector for sensing an edge of drive signal supplied to a control terminal of the switching element during the period of transition from turning on to off of the switching element; and a decision means for receiving a current detection signal from the current comparator to produce an output signal when the edge detector catches an edge of drive signal; wherein the decision means produces the different output signals of respectively first and second voltage levels under the light load condition and non-light load conditions heavier than light load.