| 摘要 |
A two-terminal A.C. device is described which can be series connected with a lighting fixture to prevent overheating of the fixture in an overload condition, namely, when a lighting element exceeding the power rating of the fixture is installed. In broad terms, the device includes a bidirectional, self-extinguishing switch which can be triggered to conduct current between the two terminals of the device, and control circuitry operable from the voltage difference and current between the two terminals occurring in use to regulate the triggering of the switch. The control circuitry includes triggering circuitry which generates triggering signals from the voltage difference across the terminals of the device and normally applies the triggering signals to the control terminal to permit a predetermined measure of conduction. In an overload condition detection circuitry detects an overload current and activates trigger signal suppressing circuitry which temporarily suppresses the application of triggering signals to the switch thereby reducing the mean level of the current delivered to the fixture in an overload condition. In an overload condition, the lighting fixture is operated in a dim or intermittent fashion thereby indicating the overload condition to the user.
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