| 摘要 |
PURPOSE:To prevent the error due to the temperature change in the speed control circuit for the DC motor whose driving current is controlled by a current mirror circuit, by driving the current mirror circuit with the emitter follower of an NPN transistor. CONSTITUTION:A reference voltage is applied to one input of a voltage comparating circuit 12 constituted by transistors Q4, Q5, Q6, and Q7, and the output voltage of the current mirror circuit 16 is fedback to the other input thereof, thereby the counter-electromotive force of the DC motor 10 gets a constant voltage, and the motor is driven at a constant rotational speed. A transistor Q1 which drives the current mirror circuit 16 is driven by the emitter follower of the NPN transistor Q9 which responds to the output signal of the voltage comparing circuit 12. Since the NPN transistor Q9 has a high current amplification factor, the base current of Q1 becomes small, thereby the error due to the temperature change can be minimized. |
