| 摘要 |
In a power supply circuit for an electrical apparatus, comprising a power transformer having its secondary winding connected to a smoothing capacitor via a rectifying circuit and having its primary winding adapted to be applied with an ac voltage, a switching means is provided for applying the ac voltage to the primary winding only for a selected period of time in a half cycle of this ac voltage and for terminating the application of this ac voltage before an arrival of a zero crossing point of the ac voltage, whereby allowing a voltage of a time length corresponding to a current flowing through the secondary winding to be applied to the primary winding of the transformer, to thereby inhibit a flow of unnecessary exciting current to the primary side. This power supply circuit also contributes to stabilization of the dc output voltage of the power supply circuit.
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