| 摘要 |
The present invention relates to a lighting unit utilizing an energy efficient arc lamp as the main source of light supplemented by a standby filamentary lamp, the filament serving as a resistive ballast for the arc lamp during normal operation. The lighting unit is designed for functional similarity to an incandescent lamp, the filament providing immediate illumination when the lighting unit is first energized and continuing illumination until the arc lamp itself produces light. In accordance with the invention, if the arc lamp does not start within a predetermined period, the application of starting potentials produced through operation of a solid state switch and a high frequency step-up transformer is discontinued and the lighting unit rendered inactive. Exemplary means includes a positive temperature coefficient thermistor responsive to the temperature rise of the solid state switch. The solid state switch is connected in a normally off, monostable configuration and requires a trigger oscillator to generate a separate pulse for each switch conduction interval. The resistance rise in the thermistor is used to prevent trigger oscillations by causing saturation of the trigger oscillator transistor at a current level sufficient for self-heating of the thermistor. The solid state switch is latched in an off state until power is removed.
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