Browse Prior Art Database

High Voltage Write Driver

IP.com Disclosure Number: IPCOM000117648D
Original Publication Date: 1996-Apr-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 4 page(s) / 91K

Publishing Venue

IBM

Related People

Klaassen, KB: AUTHOR [+2]

Abstract

Disclosed is a high data rate write driver for magnetic recording. Unlike previous write drivers, this design has current reversal times that are not limited by the power supply voltage. An additional improvement is a method for preventing breakdown in bipolar devices driving the write head.

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High Voltage Write Driver

      Disclosed is a high data rate write driver for magnetic
recording.  Unlike previous write drivers, this design has current
reversal times that are not limited by the power supply voltage.  An
additional improvement is a method for preventing breakdown in
bipolar devices driving the write head.

      In write drivers for high data rate magnetic recording, the
inductive write head has to be driven with large currents and short
current reversal times.  The current reversal time will be
approximately
               t = L Ippk / Vhead
  where L is the head inductance, Ippk is the peak-to-peak change in
head current, and Vhead is the voltage applied across the head during
a transition.  For a given head inductance and current drive
requirement, the only way to reduce the current transition time is to
increase V head.  Previous write drivers drop a significant amount of
the power supply voltage across load resistors, current sources, and
active devices.  These voltage drops subtract from the voltage
available to the head, and thus increase the current transition time.
To compensate for this voltage loss and maintain the switching speed,
the power supply voltage must be increased.  This leads to additional
power consumption and increased operating temperature.

      Fig. 1 shows the improved write driver circuit that includes
diodes D1, D2 in series with the head current.  When the current
through the head is switched, a large transient voltage appears
across the head due to the high head inductance.  In a conventional
write driver, this transient is clamped to Vhead.  With the addition
of D1 and D2, however, the head voltage is allowed to swing above the
positive power supply durin...