Lamp output protective circuit in electronic controller

摘要

A lamp output protective circuit for an electronic controller having a first npn transistor connected to an output terminal through which a lamp is supplied with electric power, a resistor connected between the emitter of said first npn transistor and the ground, and a second npn transistor having its collector connected to the base of the first npn transistor, its emitter to the ground and its base to a point between the emitter of the first npn transistor and the resistor. The base of the first npn transistor and the collector of the second npn transistor are connected to a signal line of the electronic controller connected to a power source. The base current of the first npn transistor is controlled with the second npn transistor and the resistor in order to cut off the flow of excess current in the first npn transistor in such a manner that the second npn transistor is turned on to bypass the base current of the first npn transistor when a certain voltage is applied to the base of the second npn transistor in response to the emitter current of the first npn transistor. The resistor can be made negligible compared with the lamp resistance, enabling the first npn transistor to be protected without reducing the illumination of the lamp.