| 摘要 |
A circuit for monitoring conduction of a phase controlled, alternating current switch, e.g., a thyristor switch, looks at the voltage across the switch. This voltage has a high dv/dt whenever the switch stops and starts conducting current. The voltage detected from across the switch is processed as follows: it is differentiated to produce a train of voltage spikes of very short time duration and some lesser voltages; the lesser voltages are removed; the spikes are then amplified and extended in time duration; and finally the time extended spikes are integrated. The integrated voltage is a train of alternate positive and negative voltages averaging zero during normal switch operation. However, when the switch conducts one of the half cycles only, the integrated voltage rises in one polarity sense depending upon the half cycle conducted. A control circuit becomes operative upon the integrated voltage attaining a predetermined value to initiate a control function such as de-energize the switch.
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