CONSTANT CURRENT DRIVE CIRCUIT

PROBLEM TO BE SOLVED: To provide a constant current drive circuit in which power consumption can be reduced comparatively, significant power consumption can be concentrated to a power transistor, and heat dissipation can be treated easily. SOLUTION: A constant current depending on a constant current flowing to a transistor 20 on the input side of a current mirror flows into transistors 22-1, 22-2 and 22-3 on the output side of the current mirror. Common collector of the transistors 22-1, 22-2 and 22-3 on the output side of the current mirror are connected with the emitter of a power transistor 24 passing a load current. The load current flowing through the power transistor 24 can be determined by the transistors 22-1, 22-2 and 22-3 on the output side of the current mirror. On/off of the power transistor 24 can be determined by on/off of a transistor 28 and the base voltage of the transistor 28 is determined by a Zener diode 14. Consequently, emitter voltage of the power transistor 24 can be set at a constant voltage and the transistors 22-1, 22-2 and 22-3 on the output side of the current mirror can be constituted of relatively small transistors. COPYRIGHT: (C)2007,JPO&INPIT