SWITCHING AND DRIVING CIRCUIT FOR TRANSISTOR

摘要

PURPOSE:To keep a current on an output terminal at a constant level regardless of the current amplification factor of an NPN transistor, by constituting a constant current circuit of current mirror of the first PNP transistor, and the second PNP transistor. CONSTITUTION: The second PNP transistor Q3 constitutes of a current mirror circuit that is the constant current circuit, with the first PNP transistor transistor Q2, and the current in proportion to the current on the second PNP transistor Q3 is permitted to flow on the emitter of the first transistor Q2. Meanwhile, a voltage VBE between the base and the emitter of the transistor is kept around at 0.7V constantly even in case of the change of an emitter current, and the VBE of an NPN transistor Q1, and the VBE of the third PNP transistor Q4 go to almost the same values, and voltage drops at the third resistance R3, and at the first resistance R1 become almost equal. In this way, the current being permitted to flow on an output terminal 3 is decided only by the resistance values of the resistances R2, R3, and R1, and the voltage between the first and the second power source terminals 1 and 2, even when variance or change in the current amplification factor of the NPN transistor Q1 is generated, and an output current is regulated at a constant level. LC:first terminal LC':second terminal.