| 摘要 |
The polarity detection circuit includes a first diode with anode receiving a first phase of the AC power supply voltage and a second diode with anode receiving a second phase, opposite the first phase. The detection circuit further includes a constant-voltage power supply outputting a positive constant voltage. A first reference-voltage output circuit outputs a voltage corresponding to the constant voltage when the AC voltage of the first phase is positive, and outputs a voltage at a cathode of the second diode when the AC voltage of the first phase is negative. The detection circuit also includes a first signal output circuit that compares a first voltage, corresponding to a voltage at the cathode of the first diode, and a voltage output from the first reference-voltage output circuit and that outputs a signal indicative of polarity of the AC voltage having the first phase according to a comparison result.
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