| 摘要 |
A zero crossing detector provides an optically coupled output signal with a leading edge which occurs in the vicinity of the zero crossing point of an AC voltage waveform but no later than the zero crossing time. The circuit input includes a filter and rectifier. The filtered and rectified voltage is then applied to a complex impedance circuit with an input and an output, which provides an output lagging its input. A switching device, which may be a light emitting diode, is coupled between the output of the impedance circuit and the rectifier. Thus, when the lagging output voltage of the impedance circuit exceeds the output of the rectifier, the switching device conducts, producing the output signal.
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