Digital control of the speed of a motor by a power stage driven in discontinuous mode

摘要

A driving circuit for a voice coil motor (VCM) includes a full bridge output stage for driving the motor in a pulse width modulated (PWM) mode. A multiplexer having two inputs is coupled to respective output nodes of the full bridge output stage, with one of the output nodes providing a back electromotive force induced in the motor upon setting in a high impedance state the full bridge output stage and conducting at least one transistor connected to ground in the full bridge output stage after current through the motor has decayed to zero. A controller compares a voltage representing a desired speed of the motor with the back electromotive force, and generates a correction signal based upon the comparison. A pre-driver drives the full bridge output stage as a function of the correction signal for setting in the high impedance state, and connects one of the output nodes of the full bridge output stage to ground when a certain delay time has elapsed, and produces signals that coordinately connects the input of the multiplexer coupled to the output node of the full bridge output stage not connected to ground.