| 摘要 |
PURPOSE: A switching mode power supply is provided to be capable of preventing the generation of a surge voltage. CONSTITUTION: The switching mode power supply(301) includes a transformer(321), an input controlling portion(311), a power transistor(381), first and second rectifiers(331,332), first and second filters(341,342), a feedback portion(351), a power transistor controlling portion(361), a power source(391), and a synchronous signal controlling portion(371). The primary windings of the transformer(321) include an input winding(323), to one end of which an input voltage(Vi) is applied, and a feedback winding(325) to which energy is fed back from secondary windings. The secondary windings of the transformer(321) include first and second windings(327,328) one end of each of which is grounded. In the transformer(321), the energy is accumulated in a fly back method in the input winding(323) when the power transistor(381) is turned on, and the energy accumulated in the input winding(323) is transmitted to the first winding(327), the second winding(328), and the feedback winding(325) when the power transistor(381) is turned off.
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