BEMF rectification voltage when power supply energy fails

摘要

In a disk drive, the read-write heads of the disk drive should be parked during a power failure. The kinetic energy of the spinning rotor is used to move the head away from the disk's surface. A high voltage is produce from the low voltage spindle motor by using a BEMF voltage to step up the voltage in a voltage supply capacitor to a higher voltage by enabling or disabling a switch connected to a comparator. When the switch is turned on, it shorts the rectified voltage in the stator windings to ground in order provide a current path for a current formed in the coils by the BEMF. When the current reaches a predetermined level, the switch is turned off. The current flows through the voltage supply capacitor so that its voltage is "kicked-up" by the inductance of the windings and by the BEMF still present in the stator windings. This increased voltage is used to park the heads and to brake the motion of the spindle. Two control feedback loops are used to more efficiently enable the voltage conversion. A current comparator compares the current in coils to a reference current and turns the switch off when the current is at a predetermined level. A voltage comparator compares the voltage across the load with a reference voltage and turns the switch off when the voltage is above a predetermined value.