Patent ID: 7894223
Filing Date: 2011-02-22
Classification: H02M

Abstract:
1. A switching power supply circuit comprising: a transformer having a core comprising a magnetic material of amorphous metal, and a primary-side winding and a secondary-side winding wound around the core; a switching element series-connected to the primary-side winding of said transformer, for flowing current through the primary-side winding of said transformer according to a pulsive drive signal; a primary-side current detection circuit for detecting the current flowing through the primary-side winding of said transformer; plural circuit elements for rectifying and smoothing a voltage generated in the secondary-side winding of said transformer to generate an output voltage; and a control circuit for generating said drive signal based on at least a detection result of said primary-side current detection circuit, and limiting a period for flowing the current in the primary-side winding of said transformer, wherein: said switching element includes an N-channel MOSFET (metal oxide semiconductor field effective transistor) having a drain connected to the primary-side winding of said transformer and a gate to which said drive signal is applied; and said primary-side current detection circuit includes a bipolar transistor having a base to which a voltage is applied from the drain of said MOSFET, for performing an emitter-follower operation, and detects the current flowing through the primary-side winding of said transformer by measuring a voltage between the drain and a source of said MOSFET.