| 摘要 |
PROBLEM TO BE SOLVED: To improve surge voltage and switching noise produced when a first switch element is turned off and allow the switch operation to be handled by software, by connecting a circuit for producing pulses with specified pulse width between the output terminal of an oscillation control circuit and the control electrode of a second switch element. SOLUTION: Exciting energy is accumulated in a second transformer 11 by current passed through the primary winding 11a of the second transformer 11 during the on-duration of a second switch element 12. When the second switch element 12 is turned off, the exciting energy flows the secondary winding 11b through a second diode 16 to a first capacitor 15 and is stored there. Since the on-duration of the second switching element 12 is set to a specified value, the stored voltage is in proportion to the voltage of a direct-current power supply 1. The number of turns of the tertiary winding 2c of a first transformer 2 is matched with that of the primary winding 2a and further the on-duration of the second switch element 12 is selected so that the charging voltage of the first capacitor 15 is twice the voltage of the direct-current power supply 1.
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