Browse Prior Art Database

Disk Drive DC Motor Braking Circuits

IP.com Disclosure Number: IPCOM000035237D
Original Publication Date: 1989-Jun-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 3 page(s) / 76K

Publishing Venue

IBM

Related People

Hanson, CC: AUTHOR [+2]

Abstract

The circuits described are used in disk files to brake the spindle to a stop at either power down or on request. Braking the spindle is required to reduce wear on the disk file heads which results from contact with the disks as the spindle velocity drops below the head-flying speed. To brake the spindle, the DC motor phases can be shorted to a common point. This causes the back EMF (electromotive force) voltage to be shorted, which actively slows the motor to a stop.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 53% of the total text.

Page 1 of 3

Disk Drive DC Motor Braking Circuits

The circuits described are used in disk files to brake the spindle to a stop at either power down or on request. Braking the spindle is required to reduce wear on the disk file heads which results from contact with the disks as the spindle velocity drops below the head-flying speed. To brake the spindle, the DC motor phases can be shorted to a common point. This causes the back EMF (electromotive force) voltage to be shorted, which actively slows the motor to a stop.

The solution to the braking problem is to use FET devices as drivers for the DC motor and also use these drivers to short the windings together to brake the motor. This takes advantage of the fact that FETs are voltage-driven devices and only require a low power signal to be driven into saturation. The low resistance of the FET is used to essentially short the motor phase windings together. A capacitor and diode are used to store the energy after the power-down. Two methods can be used to bias the drivers on to short the windings by using the voltage stored in the capacitor.

(Image Omitted)

In the first method, the circuit of Fig. 1 shows MOSFET drivers for a three- phase delta wound, brushless motor. The P-channel MOSFET devices, Q1, Q2 and Q3, require a negative voltage from gate to source to bias the device on (Vgs = -4V for turn-on). When the power is turned off (12 V inputs go to 0 V), VA = 0 volts and VB = 12 volts - V diode drop or approximately +11.3 volts. The voltage from gate to source on Q1, Q2 and Q3 is -11.3 volts (0 -VB). This turns Q1, Q2 and Q3 on hard into saturation, effectively shorting the motor windings, causing the braking effect. This is also done when the run/stop line goes lower than the Vref on the comparator. The N-channel devices Q4, Q5 and Q6 are turned off. They need positive voltage from gate to source to be biased on. The voltage from Vgate to source N-channel on the devices = 0 volts. The capacitor voltage only discharges due to leakage currents in the diode and its own leakage currents. This enables the three drivers Q1, Q2 and Q3 to remain turned on for more than the time needed to brake the motor to a stop (capacitor charge held...