Browse Prior Art Database

Sensefet Current Driver

IP.com Disclosure Number: IPCOM000101343D
Original Publication Date: 1990-Aug-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 2 page(s) / 51K

Publishing Venue

IBM

Related People

Commander, RD: AUTHOR

Abstract

A commercially available power MOSFET, of the type known as SENSEFET, is used to provide a high power current driver without the need for a series current sense resistor, thus avoiding the associated voltage loss and unwanted heat generation.

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Sensefet Current Driver

       A commercially available power MOSFET, of the type known
as SENSEFET, is used to provide a high power current driver without
the need for a series current sense resistor, thus avoiding the
associated voltage loss and unwanted heat generation.

      Traditionally, current drive power amplifiers, such as are used
to drive disk file actuator motors, have needed a current sense
resistor in series with the load to provide feedback of load current.
To maintain accuracy over a wide current range, this resistor often
needs to be an appreciable fraction of the load resistance, hence
incurring significant power and drive voltage losses.  The recent
availability of 'SENSEFETS' (i.e., power MOSFETS in which a few of
the thousands of identical FET cells are dedicated to providing an
accurate fraction of the current in the main FET, through a separate
terminal using an operational amplifier (op amp)) have provided the
possibility of eliminating this sense resistor.

      Alternatively, if the op amp is replaced by a comparator, the
circuit can function as a current-limited switch.  In this case, the
comparator will turn the FET hard on unless the sense terminal
current exceeds Iin, when the FET will be switched off.

      This disclosure describes an alternative op amp configuration
to both sense the current and to drive the FET.  The SENSEFET
typically provides a current of the order of 1/2000 of the main
source current at its sense...