EFFICIENT TRANSITION FROM CLASS D TO LINEAR OPERATION IN DUAL-MODE VOICE COIL MOTOR CONTROLLERS

A dual-mode positioning driver for a voice coil motor in a disk drive system is disclosed. Linear prestage drivers and pulse-width-modulated prestage drivers are both coupled to power transistors arranged in an “H” bridge for driving the voice coil motor. The positioning driver is thus operable to drive the power transistors in either a linear mode or a pulse-width-modulated class D mode. In a transition period while switching from the pulse-width-modulated mode to linear mode, comparators compare the phase voltages in the “H” bridge with a reference voltage. The outputs of the comparators are applied to the PWM output amplifiers to drive the power transistors, so that the phase voltages are preconditioned toward their linear bias points. Discontinuities in the drive current through the voice coil motor are minimized as a result.