A disk drive is disclosed comprising a head, a disk and a spindle motor for rotating the disk. An internal supply voltage is generated from a back EMF (BEMF) voltage across the windings of the spindle motor. The internal supply voltage is applied to a voice coil motor for use in parking the head during a spin-down mode. The internal supply voltage is compared to a threshold in order to activate a demand limit control signal. A periodic signal periodically disconnects the internal supply voltage from the VCM while the demand limit control signal is active.