| 摘要 |
The zero-crossing identification circuit includes a pulse delay unit which is tuned to the mains frequency. A third monostable multivibrator (M3) is provided with a working time, which lies between the cycles of the smaller and the larger mains frequency, for the differentiation of a smaller and a larger mains frequency to the pulse delayer. A fourth monostable multivibrator (M4) is connected to the third monostable vibrator, with a working time, which is larger than the cycles of the smaller mains frequency. Both monostable multivibrators have a circuit in the form of a diode (D3,D4) connected between the time determining capacitor C3,C4) and the input connection. The output of the fourth multivibrator is connected with a switching input of the pulse delay unit (M1), for the changeover of the delay time.
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