Browse Prior Art Database

ANALOG SIGNAL RECOVERY THROUGH LOSSLESS CURRENT SENSING

IP.com Disclosure Number: IPCOM000005956D
Original Publication Date: 1990-Oct-01
Included in the Prior Art Database: 2001-Nov-20
Document File: 2 page(s) / 79K

Publishing Venue

Motorola

Related People

Donn Dengel: AUTHOR

Abstract

Most applications for lossless current sensing involve detection of overcurrent conditions in power switching cir- cuits. Current-sensing MOSFETs contain two current sensing terminals (MIRROR and KELVIN) in addition to the DRAIN, SOURCE and GATE terminals. A voltage which is linearly proportional to the drain current appears at the MIRROR and KELVIN terminals. These terminals are connected to external protection circuits which turn off the MOSFET when ex- cessive drain current is detected to prevent damage to the MOSFET and its load.

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MQTdROLA Technical Developments Volume 11 October 1990

ANALOG SIGNAL RECOVERY THROUGH LOSSLESS CURRENT SENSING

by Dorm Dengel

   Most applications for lossless current sensing involve detection of overcurrent conditions in power switching cir- cuits. Current-sensing MOSFETs contain two current sensing terminals (MIRROR and KELVIN) in addition to the DRAIN, SOURCE and GATE terminals. A voltage which is linearly proportional to the drain current appears at the MIRROR and KELVIN terminals. These terminals are connected to external protection circuits which turn off the MOSFET when ex- cessive drain current is detected to prevent damage to the MOSFET and its load.

   However, applications for current-sensing power MOSFETs need not be limited to overcurrent fault detection. Since the sense voltage is linearly proportional to the MOSFET drain current, these devices may also be used for recovering the analog component of complex signal waveforms, such as in DC motor control or as part of a feedback circuit for maintaining linearity in RF power amplification.

   In a particular motor control application (see FIG. 1) a current-sensing power MOSFET switches current in a DC motor which controls the position of a screw assembly. A current sensing circuit is used to determine the position of the screw assembly. Commutator current pulses from the motor appear in the drain circuit of the MOSFET as the motor shaft rotates. These current pulses also appear as voltage pulses on the M...