| 摘要 |
With an ignition key inserted in a key holder, even though a tail light is not turned on, when it is dark at night, the resistance value of a photo conductive cell(CdS) of a brightness detector(10) is maintained high. Therefore, the base bias power source of a transistor(Q) is kept to be low level and the transistor maintains off status, so, a relay terminal(Re) is on. And as the tail light is powered, the tail light is lighted up. When it is dark at night, and the driver pulls out the ignition key from the key holder after parking, the key switch is off that the driver is capable of driving safely, preventing the loss of power.
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