| 摘要 |
A switching power supply circuit includes a DC/DC converter, a control circuit, a first auxiliary power supply circuit, and a second auxiliary power supply circuit. The DC/DC converter has a transistor for switching a DC input voltage. The control circuit controls the ON/OFF time of the transistor to keep a DC output voltage from the DC/DC converter constant. The first auxiliary power supply circuit supplies power to the control circuit during a normal switching operation period of the transistor. The second auxiliary power supply circuit supplies power to the control circuit when a DC input voltage is applied to the switching power supply circuit. The second auxiliary power supply circuit is controlled by an output voltage from the first auxiliary power supply circuit to stop the supply of power.
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