Patent ID: 8885365
Filing Date: 2014-11-11
Classification: H02M

Abstract:
1. A switching power supply device comprising: a transformer that includes a primary winding, a secondary winding, and a tertiary winding, where the primary winding is connected to an input voltage; a switching element connected to the primary winding; an output voltage generating unit that outputs an output voltage according to a secondary winding voltage generated in the secondary winding; an output voltage detecting unit that generates an output voltage detection signal representing the output voltage according to a detected voltage on the tertiary winding; and a control unit that controls switching the switching element on and off according to at least the output voltage detection signal, such that the output voltage is controlled to be a predetermined voltage, wherein the output voltage detecting unit compares the detected voltage with a first reference value in a first comparison, differentiates the detected voltage to provide a differentiated value, compares the differentiated value with a second reference value in a second comparison, and determines a start and an end of a detection period on the basis of results of the first and second comparisons, the output voltage detecting unit samples and holds the detected voltage with a first sampling pulse and a second sampling pulse within the detection period, and when the detection period ends, the output voltage detecting unit selects one of the two sampled and held voltages and outputs the selected voltage as the output voltage detection signal.