Speed control apparatus for DC motor

摘要

A speed control apparatus for DC motor (1), comprises a bridge circuit formed by the winding of the motor (1), a resistor (2) series thereto, and two resistors (3 and 4). Therein, a reference voltage (Er) is produced by dividing a voltage Vref of a constant voltage circuit (20) by a divider network (21+22). The voltage difference this reference voltage (Er) and a voltage produced across the detection output terminals "a" and "b" which is proportional to a counter electromotive force (Ea) of the DC motor (1) is amplified by a differential amplifier (23+24). A current mirror circuit is formed by transistors (16), (17) and (18). The first transistor (16) regulated of its collector current (Ir) by a constant current circuit (19) controls collector current of the second transistor (17), which controls input current of the constant voltage circuit (20). The third transistor (18) regulated of its collector current constantly controls the input current to the differential amplifier (23+24) for controlling the transistor (7) to control the motor current.