Patent ID: 6664817
Filing Date: 2003-12-16
Classification: G01R,H02M,H03K

Abstract:
A zero-cross detection circuit connected to a power supply device, the power supply device including:a full-wave rectifying and smoothing circuit powered via first and second lines from a commercial AC power supply for full-wave rectification and smoothing; two capacitors having first ends connected to a high-voltage output terminal and a low-voltage output terminal of the full-wave rectifying and smoothing circuit, respectively, and second ends connected to a ground; and a switching regulator for separating and stepping down the output from the full-wave rectifying and smoothing circuit to output a desired DC voltage, said zero-cross detection circuit comprising: a transistor, having an emitter, a base, and a collector, of which the emitter is connected to the low-voltage output terminal of the full-wave rectifying and smoothing circuit for outputting a zero-cross detection signal from the collector; a first resistor connected between the base and emitter of the transistor; a second resistor connected between the first line and the base of the transistor; and a third resistor connected between the second line and the emitter of the transistor.