A disk drive system including retract logic for control of the voice coil motor in a retract operation, in which the voice coil motor positions the read/write head actuator arm in a safe place in a loss-of-power event, is disclosed. The retract logic includes circuitry for controlling the application of power to the voice coil motor from an external capacitor, so that a constant voltage is maintained across the voice coil motor. Current from the capacitor is directed to an internal variable resistor that conducts a selected current, in parallel with the current applied to the voice coil motor. The voltage developed across the variable resistor is applied to one input of a control amplifier, which receives the voltage across the voice coil motor at another input; the control amplifier in turn controls the gate of a low side transistor. The transistor passes current to the extent that the voltage across the voice coil motor corresponds to that developed across the variable resistor.