| 摘要 |
PROBLEM TO BE SOLVED: To provide a power supply capable of reducing an input power at no load by utilizing the fact that the current flowing a light receiving element of a photocoupler for sending a feedback signal to a primary side comes to be maximum when a secondary side bears no load. SOLUTION: A switching regulator stabilizes the output voltage on the secondary side by detecting a voltage on the secondary side and transmitting a feedback signal to an oscillation control circuit on the primary side through the photocoupler. A first resistor which converts the current flowing through the light receiving element of the photocoupler into a voltage is inserted. The voltage across both ends of the resistor reaches the base-emitter voltage of a transistor when the load on the secondary side comes to be zero, to allow the transistor come into the on state. A capacitor is connected which charges the current flowing through a collector of the transistor when the transistor comes to the on state. Further, a second resistor is connected between the capacitor and a control signal input terminal of the oscillation control circuit, so that discharging of the electric charge of the capacitor is provided with a time constant. COPYRIGHT: (C)2004,JPO
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