| 摘要 |
In order to protect a valve (thyristor 1) against overvoltages, the valve voltage is monitored by means of a break-over element (BOD) which connects the operating voltage to the control connection of the valve when its break-over voltage is exceeded, and causes emergency triggering. The valve voltage additionally charges a capacitor (4) which is connected in parallel with the valve but which is discharged when the break-over element (BOD) breaks over, via the light-emitting diode (6) of an optocoupler and the switched-through break-over element. A feedback signal, which if necessary is amplified on a transistor (9), is picked off on the photo-element (8) of the optocoupler (7). <IMAGE>
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