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SENSEFET LINEAR POWER SUPPLY

IP.com Disclosure Number: IPCOM000005682D
Original Publication Date: 1987-Oct-01
Included in the Prior Art Database: 2001-Oct-25
Document File: 1 page(s) / 59K

Publishing Venue

Motorola

Related People

Kathy Recktenwald: AUTHOR [+3]

Abstract

A circuit 10 operates as a linear power supply. A first stage 11 is a voltage tracking circuit. It essentially consists of avoltage reference device TL431, an op amp Ll, a transistor Ql, aSenseFETT1, and a resistor voltage divider.

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MOTOROLA Technical Developments Volume 7 October 1967

SENSEFET LINEAR POWER SUPPLY

by Kathy Recktenwald, Tim Ruther and Randy Scott

   A circuit 10 operates as a linear power supply. A first stage 11 is a voltage tracking circuit. It essentially consists of avoltage reference device TL431, an op amp Ll, a transistor Ql, aSenseFETT1, and a resistor voltage divider.

   Op amp Ll compares a fraction (one half) of the SenseFET Ti output source voltage (V,,) to a constant reference voltage REF. The output of Ll controls the base current of Ql. Ql varies the gate(G) voltage of SenseFET Tl so as to maintain V,, at a constant level.

A second stage 12 is essentially a parallel-connected current mirror of the 1st stage 11. It consists of an error amplifier L2, a transistor Q2, a SenseFET T2, and a capacitor C2.

   Current mirror voltages related to the source currents of Tl and T2 are fed into L2. The output of L2 varies the base current of Q2, and the transistor Q2 varies the gate voltage of SenseFET T2. The result is that the conduction of T2 will be controlled so as to match that of Tl.

Integrating the output of error amplifier L2, via C2, dampens out oscillations due to the current sharing of Tl and T2 that normally occur if C2 were not present.

   The circuit 10 essentially provides the SenseFETs Tl and T2 as two power output devices connected in parallel to provide a regulated output voltage V,, with high current capability. The circuit configuration insures equal current sh...