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Clamps to Limit Head-To-Disk Voltage in Arm Electronics Chip

IP.com Disclosure Number: IPCOM000119314D
Original Publication Date: 1991-Jan-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 2 page(s) / 67K

Publishing Venue

IBM

Related People

Swart, DP: AUTHOR

Abstract

A preamplifier circuit is shown to which clamp transistors are added which limit the read element to disk voltage in a direct access storage device (DASD) file. Element to disk voltage must be limited to prevent head element damage due to arcing or metal migration.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Clamps to Limit Head-To-Disk Voltage in Arm Electronics Chip

      A preamplifier circuit is shown to which clamp
transistors are added which limit the read element to disk voltage in
a direct access storage device (DASD) file.  Element to disk voltage
must be limited to prevent head element damage due to arcing or metal
migration.

      READ PREAMP:  (See the figure.) The read preamp contains a
control loop which consists of amplifier 9, PNP base drive circuit
13, and preamp front end 14.  The loop's function is to keep the
head's voltage at node 19 equal to the disk voltage.  However, the
loop is slow, and during power-up and head switching transients, the
loop loses control for tens of microseconds.  The head-to-disk
voltage can become large (greater than 1.0 volt) during this period.

      If the head should hit a conductive bump on the disk during
this uncontrolled period, the head can be damaged. Thus, it is
imperative that the head-to-disk voltage be clamped.

      The figure shows the read preamplifier circuit.  Only the clamp
network consisting of resistors 1, 3 and 4, diode 2, and transistors
5 and 6 are claimed in this disclosure. The other parts are included
to complete the description.

      A voltage divider consisting of resistors 1, 3 and 4 and diode
2 determines the voltage on the disks, which are tied to output node
8.  Clamp transistors 5 and 6 tie into the same voltage divider, and
limit the voltage excursions of node 17 with respect...