| 摘要 |
PROBLEM TO BE SOLVED: To provide a switching power supply control circuit preventing rapid increase of on-duty with a simple circuit structure and preventing influence to a control circulation characteristic of a whole power circuit at the time of a regular operation. SOLUTION: The control circuit includes an active clamp circuit 22, a main switch element SW1 switching power input voltage, a comparator 14 ouputting a PWM signal and a triangular wave generating circuit 18 connected to one input terminal of the comparator 14. A photo coupler PC outputting a negative feedback signal is connected to the other input terminal of the comparator 14. On-duty of the main switch element SW1 is controlled to a duty ratio which is set by the comparator 14. A cathode of a first diode D3 and an anode of a second diode D4 are connected to an output side of the photo coupler PC. An anode of the first diode D3 is connected to a cathode of the second diode D4. A connection point and one terminal of a capacitor C2 are connected in series. COPYRIGHT: (C)2008,JPO&INPIT
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