| 摘要 |
PROBLEM TO BE SOLVED: To constitute a synchronous rectifying-type forward converter to be stably operated by reducing a stress on a switching element for synchronous rectification even if a reverse operation by an output overvoltage or a self-oscillation occurs. SOLUTION: A switching element Q5 for communication switch turn-off control is connected to an auxiliary winding N4 of a main transformer T1 in series. A charged electric charge of a gate/source capacitance of a communication switching element Q3 is controlled by the switching element Q5. A control switching element driving circuit 24A turns on the switching element Q5 when a main switching element Q1 is turned on. A primary-side control stop detection circuit 25A detects a control stopping state of a switching control circuit 23 on the basis of an output signal from the control switching element driving circuit 24A. If the primary-side control is stopped, an on-signal intermittent switching element Q7 is conducted to turn on the switching element Q5, so that the electric charge of the gate/source capacitance of the communication switching element Q3 is immediately discharged. COPYRIGHT: (C)2007,JPO&INPIT
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