SPEED CONTROL CIRCUIT FOR MOTOR

PURPOSE:To improve precision of a D/A converter, by reducing the voltage applied to a full-scale decision terminal of the D/A converter when an analogue target value to be outputted from the D/A converter is smaller than the set value. CONSTITUTION:A microcomputer 10 outputs a 10V selection signal S1 when an analogue target value outputted from a D/A converter 2 is not less than the set value e.g. +5V. It outputs 5V selection signal S2 when this analogue target value is smaller than the set value. Analogue switches 11 and 12 apply +5V and +10V DC voltage to a fullscale decision terminal VREF of the D/A converter 2 by these selection signals S1 and S2. The output of the D/A converter is given to a drive circuit 16 through an error amplifier 13 and a motor 15 is driven with it.