| 摘要 |
PROBLEM TO BE SOLVED: To increase the light-load-time conversion efficiency of a RCC system switching power device 31, and to enhance its response from a light-load to a heavy load. SOLUTION: A voltage detecting circuit 45 outputs an oscillation stop signal when a secondary output voltage is not lower than a reference voltage, and outputs an oscillation start signal when it is lower. A load detecting circuit 43 performs load detection on the basis of voltage generated in a control winding N3. An oscillation control circuit 44 makes the output of the voltage circuit 45 valid while lightly loaded, responds to the oscillation stop signal to turn TR6 on and bypass a RCC pulse, responds to the oscillation start signal to turn TR6 off, and gives the RCC pulse to Q to cause it to perform burst oscillation. The frequency of oscillation on the occasion of burst oscillation is equal to that on the occasion of being usually loaded, and becomes an optimum frequency determined by a load RL and the primary winding N1 of a transformer N, and its efficiency becomes high. Besides, it is possible to reduce the variation of output voltage sharply having an excellent response, since an oscillation stop period becomes shorter as the load becomes heavier.
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