| 摘要 |
A series circuit of a primary winding 1 A of a transformer 1 and a switching element 2 is coupled to a DC source 3 and a voltage induced in a secondary winding 1B of the transformer 1 according to switching operation of the switching element 2 is rectified and smoothed by a rectifier smoothing circuit 9. Further, a Zener diode 21 is coupled across the switching element 2 with reverse polarity to the switching element 2. The Zener diode 21 may be coupled across a rectifier diode 5 which conducts during the ON period of the switching element 2.
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