Browse Prior Art Database

Position Control Motor Driver with Dead-Band Avoidance Circuit

IP.com Disclosure Number: IPCOM000116590D
Original Publication Date: 1995-Oct-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 45K

Publishing Venue

IBM

Related People

Enami, K: AUTHOR

Abstract

Disclosed is a circuit for position control motor drive with dead-band avoidance means. It is suited for Voice Coil Motor (VCM) driver of hard disk drive. It can also avoid poor servo stability with dead-band of the driver.

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Position Control Motor Driver with Dead-Band Avoidance Circuit

      Disclosed is a circuit for position control motor drive with
dead-band avoidance means.  It is suited for Voice Coil Motor (VCM)
driver of hard disk drive.  It can also avoid poor servo stability
with dead-band of the driver.

      Fig. 1 shows a block diagram of the VCM driver.  Fig. 2 shows
the output stage of the amplifier A and amplifier B in Fig. 1.

      A bias current circuit that consists of FET Q6 - Q14 and RS
flipflop FF1 is featured.  When Pch power FET Q1 is active, Q14 is
also activated by this bias current circuit.  The bias current Ibn is
determined by standard current Isn and a current mirror circuit, Q12
and Q14.  In the same way, when Nch power FET Q2 is active, bias
current Ibp is added to the current of Q2.

      Fig. 3 shows typical drain current vs input voltage.  When Q2
is active and the input voltage is increasing from the negative area,
a dead-band exists between Point a and b in the graph.  But if the
input once exceeds Point b, the operating point jumps to Point c.  At
Point c, there is no dead-band as long as the input does not decrease
to Point d again.  Therefore, if this hysteresis is large enough to
cover the normal alternating operation current for VCM control during
track-following, then the risk that the operating point remains at
the dead-band, is significantly lower with any bias force of VCM.