| 摘要 |
<p>In a power supply device including a full-wave rectifying and smoothing circuit powered from a commercial AC power supply via two power supply lines, a switching regulator for separating and stepping down the output from the full-wave rectifying and smoothing circuit to output a desired DC voltage, and two capacitors (C12,C13) after the full-wave rectifying and smoothing circuit for the terminal noise suppression purpose, a zero-cross detection circuit includes a transistor (Q41) 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 (R43) is connected between the base and emitter of the transistor; a second resistor (R41) is connected between one of the power supply lines and the base of the transistor; and a third resistor (R42) is connected between the other power supply line and the emitter of the transistor.
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