| 摘要 |
PURPOSE:To prevent switching transistors in a keying circuit from breaking down by detecting the charging voltage of a smoothing capacitor and boosting the voltage when the detected is over the prescribed voltage to feed back it to a smoothing capacitor of a rectifier circuit. CONSTITUTION:Since a circulating current flows every time the polarity is changed, the charging voltage of the smoothing capacitor 11 rises gradually. When the voltage is made to over the prescribed voltage, a comparator 28a of a DC-DC converter 28 outputs the difference. Moreover, the voltage in proportion to the size of the difference is fed back to the smoothing capacitor 3 as the output of the DC-DC converter, Namely, the power supplied to the input side of the DC-DC converter is supplied to the smoothing circuit 3 of the first rectifier circuit. By this method, a part of the energy accumulated in the smoothing capacitor 11 is returned to a primary side of a transformer 7 and the charging voltage of the capacitor 11 drops. Accordingly, the switching transistors 12-15 are prevented from breaking down based on the charging voltage of the smoothing capacitor 11.
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