| 摘要 |
PURPOSE:To increase a life of a lamp connected between a control transistor and a battery wherein the lamp is turned on and off, by forming a circuit so as to drive the lamp with constant current, and thereby enabling the lamp to be turned on without being affected by fluctuation in voltage of the battery. CONSTITUTION:An emitter of an input transistor T1 is grounded, and a signal input is applied through a resistor R1 to a base of the transistor T1. A collector of the transistor T1 is connected through a resistor R3 to a power supply VCC, and is also connected to a base of a control transistor T2. A lamp L and a diode D are connected in series between a collector of the transistor T2 and a battery B. A resistor R4 is interposed between an emitter of the transistor T2 and the earth. Voltage of the base of the transistor T2 is suppressed to a level not more than a fixed voltage by means of a Zener diode ZD. Anode of the Zener diode ZD is grounded, while cathode is connected to the base of the transistor T2. |
