| 摘要 |
PROBLEM TO BE SOLVED: To prevent production of surge voltage, by, when a synchronizing signal is applied in response to a voltage produced in a feedback winding, turning on a power transistor immediately after the power transistor is turned off. SOLUTION: A synchronizing signal control section 371 is connected between the other end of a feedback winding 325 and a power transistor control section 361. When a synchronizing signalΦsync is applied in response to a feeding stringing voltage Ve produced from the feedback winding 325, the synchronizing signal control section 371 turns on a power transistor 381 immediately before the power transistor 381 is turned on after it is turned off, or immediately after the power transistor 381 is turned on. Immediately after the power transistor 381 is turned on, a synchronizing voltage Vsynct reaches the value of a voltage applied to the inverting input terminal (-) of the first comparator of the power transistor control section 361. As a result, first and second rectifiers 331, 332 can be protected in safety.
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