| 摘要 |
A contactless motion detector, such as an oscillator sensitive to an approaching metallic element, is connected across a storage capacitor which can be charged from a source of pulsating direct current through a constant-current unit whose current flow is throttled when the charging voltage of the capacitor reaches a predetermined level. A thyristor connected across the series combination of storage capacitor and constant-current unit has a gate connected to a tap on a voltage divider lying in parallel with the capacitor so as to fire when the capacitor voltage rises substantially above the aforementioned level in order to break down a Zener diode forming part of that divider. Such a rise occurs when a transistor, inserted between the capacitor and a higher-voltage output of the constant-current unit, is turned on by a switching transistor responsive to a trigger signal from the detector. Untimely firing of the thyristor due to voltage fluctuations in the supply circuit can be prevented by an ancillary transistor, responsive to the same trigger signal, which normally either cuts off a protective transistor between the capacitor and the thyristor gate or establishes a shunt path in parallel with the voltage divider and the storage capacitor. |
