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Voice Coil Motor "Go Home" Circuit

IP.com Disclosure Number: IPCOM000102316D
Original Publication Date: 1990-Nov-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 2 page(s) / 51K

Publishing Venue

IBM

Related People

Enami, K: AUTHOR

Abstract

Disclosed is a circuit which makes read/write head(s) in a hard disk file go to a home position by driving a voice coil motor (VCM) when a power supply is cut off. This function saves a data area on magnetic disk(s) from damage by head/disk contact. The circuit supplies a limited current to the VCM and makes the head(s) go home surely and safely.

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Voice Coil Motor "Go Home" Circuit

       Disclosed is a circuit which makes read/write head(s) in
a hard disk file go to a home position by driving a voice coil motor
(VCM) when a power supply is cut off.  This function saves a data
area on magnetic disk(s) from damage by head/disk contact.  The
circuit supplies a limited current to the VCM and makes the head(s)
go home surely and safely.

      The drawing shows this circuit.  The circuit comprises two FETs
Q1 and Q2, two transistors Q3 and Q4, two diodes D1 and D2, and
several passive parts.

      When the power supply voltage is down, a power monitor circuit
turns the transistor Q4 off.  Then, the voltage of capacitor C2 turns
the transistors Q1 and Q2 on.  A current caused by the electro-motive
force of a spindle motor go through the VCM, and it causes the
head(s) to go home.

      In this operation, if the current is larger, the VCM crushes
into a stopper which limits the travel range of the VCM. The hard
impact by the head could damage the disk surface.  If the current is
less, the head(s) cannot be returned to the home position correctly.
Therefore, a control of this current is very important, and a
constant proper current value is required.

      In this circuit, the transistor Q3 with a current sensing
resistor R1 limit that peak current by the gate voltage control of
the FETs Q1 and Q2.  The current is limited to the value which is
fixed by resistor R1 and a base-emitter voltage of...