초록 ▼

A switched-mode power supply circuit having an operating mode and a stand-by mode. The switched-mode power supply circuit includes a transformer and a controllable switch connected to a primary winding of the transformer for switchably connecting the primary winding to a source of d.c. voltage. In t

A switched-mode power supply circuit having an operating mode and a stand-by mode. The switched-mode power supply circuit includes a transformer and a controllable switch connected to a primary winding of the transformer for switchably connecting the primary winding to a source of d.c. voltage. In the stand-by mode, the switched-mode power supply circuit is arranged to switchable connect the primary winding to the d.c. voltage source in bursts which occur at a low frequency. Between each of the bursts, an auxiliary capacitor, which is ordinarily charged by an auxiliary winding during switching of the controllable switch, is now charged by a start-up current source contained in a controller for controlling the controllable switch.

대표청구항 ▼

[ What is claimed is:] [1.] A switched-mode power supply circuit having an operating mode and a stand-by mode, said switched-mode power supply circuit comprising:means for generating a d.c. supply voltage having a first output terminal and a second output terminal;a transformer having a primary wind

[ What is claimed is:] [1.] A switched-mode power supply circuit having an operating mode and a stand-by mode, said switched-mode power supply circuit comprising:means for generating a d.c. supply voltage having a first output terminal and a second output terminal;a transformer having a primary winding, an auxiliary primary winding, a first secondary winding and a second secondary winding, said primary winding having a first terminal coupled to the first output terminal of said generating means, and a second terminal;a controllable switch connected in a series with the second terminal of said primary winding and the second output terminal of said generating means;a main output capacitor coupled across output terminals of said first secondary winding for providing a first main output voltage in the operating state and a second main output voltage in the stand-by mode, said second main output voltage being lower than said first main output voltage;a control output capacitor coupled across output terminals of said second secondary winding for providing a control output voltage;means for selectively coupling one of the output terminals of said first secondary winding to said second secondary winding during said stand-by mode;an opto-coupler having light emitting means and light detecting means optically coupled to said light emitting means;means for selectively coupling the light emitting means of said opto-coupler across said control output capacitor during said stand-by mode;means for causing said light emitting means to emit light to said light detecting means when the control output voltage across said control output capacitor exceed a predetermined value during said stand-by mode; anda controller having an output for supplying switching signals to said controllable switch, an auxiliary voltage sensing input coupled, via a shunting auxiliary capacitor, to said auxiliary primary winding of said transformer, and a stand-by mode detecting input coupled to an output of said light detecting means, said light detecting means having an input coupled to receive said auxiliary voltage, said controller comprising a start-up current source for charging said auxiliary capacitor during start-up of said switched-mode power supply, whereby, during said stand-by mode, said stand-by current source is used to intermittently charge the auxiliary capacitor when said controllable switch is not switching.