Patent ID: 6178100
Filing Date: 2001-01-23
Classification: H02M,Y02B

Abstract:
A switching power source, which is a switching power source of a ringing choke converter system, comprising:a transformer for accumulating excited energy during an on-period of a main switching element;an output circuit for outputting the excited energy thus accumulated during an off-period of the main switching element, the output circuit being placed on the secondary side of the transformer;a first capacitor which is placed between a control coil of the transformer and the control terminal of the main switching element, and which feeds back a ringing pulse that occurs in the control coil upon completion of the output of the excited energy to the control terminal after cutting a dc component thereof so that the main switching element is on driven;a series circuit which is constituted by a reverse-bias voltage setting resistor and a control switching element for reducing switching frequency, and has a first end connected to a point between the first capacitor and the control terminal of the main switching element and a second end connected to the first capacitor through the control coil;a bias resistor that is interpolated between the first capacitor and the main switching element; anddecision means for making a judgment as to whether or not load is light or heavy so that the control switching element is on-driven at the time of light load and the control switching element is off-driven at the time of heavy load, wherein:in the case when the control switching element for reducing the switching frequency is on-driven at the time of light load, during the on-period of the main switching element at the time of light load, a charge is accumulated in the first capacitor by a voltage induced in the control coil; and at the time of occurrence of the ringing pulse, a reverse bias is generated by the accumulated charge in the first capacitor so as to prevent the main switching element from being on-driven.