US 5,504,402 A · BEMF rectification voltage when power supply energy fails

Abstract

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.

Claims17

Dependent claims

A motor driver circuit, capable of applying an increased load voltage to a load when an interruption in a primary power supply occurs, the increased load voltage being produced from a BEMF of the windings of a polyphase motor, comprising:

a plurality of driver transistors, each having a conduction path coupled between a power supply node and an associated winding of the polyphase motor, and having a control electrode driven according to a commutation sequence;
load voltage storage means, coupled to the power supply node, for storing a load voltage and for applying the load voltage to the load;
switch means, coupled to the power supply node, coupled across the load voltage storage means, and having a control electrode, for selectively shunting a current produced from the BEMF generated by a coasting rotor of the polyphase motor from being applied to the load voltage storage means;
and
control means, coupled to the control electrode of the switch means, for opening the switch means responsive to a current passing through the switch means exceeding a threshold value, so that the current is applied to the load voltage storage means in such a manner that the load voltage is increased.

2 more elements

A disk drive system, comprising:

a polyphase motor, having a plurality of stator windings, and connected to a spindle for rotatably spinning at least one disk;
a head assembly having at least one read-write head cooperating with the at least one disk and being positioned by a head positioning device;
a retracting head device powered by a load voltage;
a plurality of driver transistors, each having a conduction path coupled between a power supply node that is coupled to the power supply voltage and an associated one of the plurality of stator windings, and each having a control electrode;
a sequencer, having a plurality of outputs, each coupled to one of the plurality of driver transistors, for controlling the driver transistors according to a commutation sequence, and for turning off all of the plurality of driver transistors responsive to loss of the power supply voltage;
a capacitor, coupled to the retracting head device, for storing the load voltage;
a shunt switch circuit, coupled to the power supply node and coupled across the capacitor, for selectively shunting an induced current produced from a BEMF generated in the stator windings of the motor and conducted through at least one of the plurality of driver transistors from being applied to the capacitor;
and
a control circuit for producing a switch control signal to the shunt circuit responsive to a shunt current passing through the shunt switch circuit so as to open the shunt circuit, so that the induced current charges the capacitor to an increased load voltage.

6 more elements

Dependencies are inferred from the claim text.

BEMF rectification voltage when power supply energy fails

Life of this patent

BEMF rectification voltage when power supply energy fails

Life of this patent

Abstract

Claims17