ROTATING SPEED CONTROLLING CIRCUIT

PURPOSE:To obtain a rotating speed control circuit which is affected by the variations in a load and environmental conditions by composing a speed feedback circuit of a rotating speed loop of a rotating speed detector, a rotating speed discriminator and a voltage generator for generating a voltage rising or falling as time. CONSTITUTION:A rotating speed discriminator 4 inputs a signal 40 outputted from a rotating speed detector 3, and outputs a signal 48 when the rotating speed is the lower limit or lower of an allowable range of a reference speed, a signal 49 when in the allowable range, and a signal 50 when the upper limit or higher of the allowable range. A voltage generator 5 supplies a voltage rising as time when the signal 48 is inputted, a voltage fallings as time when the signal 50 is inputted, and the voltage at that time to a drive amplifier 1 when the signal 49 is input.