| 摘要 |
PURPOSE:To obtain a power supply circuit having high working efficiency with reduction of noises and waveform distortions, by driving a switch means in response to reduction of the voltage level of a low-voltage output terminal of a power supply transformer and changing the connection between the load and the low- and high-voltage output terminals of the transformer. CONSTITUTION:The output voltage of a transformer 2 is reduced as the amplitude of the output signal of a power amplifier 16 is gradually increased. This reduction of the voltage is detected in the form of the DC voltage by rectifiers 18 and 19 and a smoothing capacitor 20. When the level of said output voltage is reduced less than the reference voltage level of a reference power supply 21, the output of an amplifier 22 is negative and a switch driving PNP transistor 25 is turned on. Then the current flows to the driving coils of both switches 10 and 11. Thus these switches 10 and 11 are closed. As a result, the low power supply voltage VL is cut automatically by the functions of rectifiers 12 and 13. Then the high power supply voltage VH is impressed to the amplifier 16.
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