Zero-cross detection circuit

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.