| 摘要 |
A power supply circuit disclosed herein includes a three-terminal regulator for stabilizing a positive voltage applied thereto, a voltage converter for converting the stabilized voltage into a negative voltage, a power-supply section for stabilizing a voltage by a light-emitting diode, and a control circuit for applying a bias voltage across a drain and source of a GaAs FET amplifier only when a voltage is being applied across the gate and source of the amplifier. When power is introduced from a power supply, the presence of the negative voltage supplied from the voltage converter is sensed by the control circuit and a bias begins to be applied to the gate. Therefore, when it is sensed that a predetermined voltage is applied to the gate, a bias begins to be applied to the drain of the FET thereafter. When power from the power supply is cut off, a drop in voltage is sensed and the drain bias begins being cut off while the gate bias for the FET is cut off thereafter.
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