Switching power supply

U.S. Patent Number: 5661642

Abstract: A switching power supply supplying power from an alternating-current power supply to a load includes a transformer having primary, secondary, and tertiary windings and a switching element, connected to the primary winding of the transformer, providing power from the alternating-current power supply to the primary winding. A control circuit controls the switching element to turn on and off. A supplementary power-supply circuit, connected to the tertiary winding of the transformer, provides output power to operate the control circuit. A start-up circuit is connected between one of output terminals of the alternating-current power supply and the supplementary power-supply circuit, and provides a current to the supplementary power-supply circuit to increase the output power of the supplementary power-supply circuit. In the switching power supply, when the output power of the supplementary power-supply circuit reaches a given value, the switching element is controlled to turn on and off, and power is generated in the secondary winding of the transformer and is provided to the load to be connected to the secondary winding.

Inventors: Shimashita; Ishio (Hadano, JP)

Assignee: Ricoh Company, Ltd. (Tokyo, JP)

Application Number: 08/564,746

Issued: 1997-08-26

Expired: 2005-08-26

Classes: 363/21.15 ; 363/21.18; 363/49

Field of search: 363/49,21,41 323/901

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