| 摘要 |
A switching power source device of resonance type is provided which comprises an output voltage detector 18 for detecting output voltage on a load 13 to produce a detection signal; and a control circuit 2 for applying on-off signals V<SUB>g1</SUB>, V<SUB>g2 </SUB>to each control terminal of first and second MOS-FETs 3, 4 in response to the detection signal from the output voltage detector 18. Control circuit 2 comprises a frequency control circuit 23 for controlling the on-off operation of first and second MOS-FETs 3, 4 in response to the level of detection signal from output voltage detector 18 to decide the switching frequency of first and second MOS-FETs 3, 4. Frequency control circuit 23 is provided with an on-time control circuit 21 which more reduces the on-span of one of first and second MOS-FETs 3, 4 during the light load period in response to the level of detection signal from output voltage detector 18 than during the non-light load period to control power consumption, reduce switching loss and noise, and improve switching efficiency in electronics.
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