Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

Voltage Boost Circuit for Servo Power Amplifier

IP.com Disclosure Number: IPCOM000082875D
Original Publication Date: 1975-Feb-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 50K

Publishing Venue

IBM

Related People

Palmer, RS: AUTHOR

Abstract

A track following servo system employs a voice coil motor (VCM) 6, with the coil connected in a bridge circuit 12a to 12d, as in Fig. 1, or in a complementary circuit 12a and 12b as in Fig. 2. The servo circuit uses a power supply that includes a voltage boost circuit.

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 63% of the total text.

Page 1 of 2

Voltage Boost Circuit for Servo Power Amplifier

A track following servo system employs a voice coil motor (VCM) 6, with the coil connected in a bridge circuit 12a to 12d, as in Fig. 1, or in a complementary circuit 12a and 12b as in Fig. 2.

The servo circuit uses a power supply that includes a voltage boost circuit.

The servo operates in the track-follow mode with a nominal voltage, +Vn and -Vn, as less current (and hence supply voltage) is required to keep the VCM actuator nulled than when seeking. C1 charges through D1, R1 and Q5 to a full 2Vn (minus the voltage drops in D1 and Q5). When a seek is desired, Q3 is turned on which turns off Q4, through speedup capacitor C2 and turns off Q5. Q3 also turns on Q2 and thereby Q1 connecting the minus side of 2Vn capacitor C1 to +Vn. Diode D1 is back biased and its cathode rises to 36 volts required by the actuator for a seek.

Once the seek is complete, Q3 is turned off as well as Q2 and Q1 and C1 is recharged through R1 and Q5. The value of R1 is determined by the minimum dwell time of the actuator, and should be as large as possible to lower the instantaneous current capacity of the Plus-Minus Vn supplies.

In the event of an emergency condition, such as a short in the power amplifier, it is desirable to shutdown the power supplies with a separate "crowbar" circuit. This is accomplished by turning both Q1 and Q5 on with switch S1, thus shorting the supplies, thereby protecting the actuator until circuit breakers CB1 an...