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VOLTAGE REGULATOR REQUIRING NO COMPENSATION CAPACITOR

IP.com Disclosure Number: IPCOM000005453D
Original Publication Date: 1982-Jan-01
Included in the Prior Art Database: 2001-Oct-10
Document File: 3 page(s) / 95K

Publishing Venue

Motorola

Related People

Gary L. Pace: AUTHOR

Abstract

A low voltage Integrated circuit requires a regulated voltage which is proportional to a transistor base-emitter voltage drop. Normally, a feedback circuit with the need for a compensation capacitor to en- sure stability would be used to implement the voltage regulator. The circuit in Figure 1 provides the re- quired voltage without the need for such acapacltor.

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Volume 2 January 1982

8 MQmmoL8a Technical Developments

VOLTAGE REGULATOR REQUIRING NO COMPENSATION CAPACITOR

By Gary L. Pace

    A low voltage Integrated circuit requires a regulated voltage which is proportional to a transistor base-emitter voltage drop. Normally, a feedback circuit with the need for a compensation capacitor to en- sure stability would be used to implement the voltage regulator. The circuit in Figure 1 provides the re- quired voltage without the need for such acapacltor.

   The circuit in Figure 1 uses two transistors, Ql and Q2, and two resistors, Rl and R2, coupled in a feedback arrangement to provide a regulated output voltage at node V2 which is directly proportional to the base-emitter voltage of Ql. Two biasing current sources, I1 and 12, are connected as shown in the Figure. For sufficiently large transistor 0, the base-emitter voltage of Ql is set by Il. During operation, the output voltage at V2 will increase until the voltage at the base of Ql developed by the voltage divider action of Rl and R2 is equal to the base-emitter voltage of Ql, VBE (al), where VBE (ai) is controlled by the bias current Il. At this time, transistor Q2 will turn on and cause the output voltage V2 to remain cons- tant. The regulator output voltage V2 is given by:

(Rl + R2)

V2= Rl VBE (Ql) (P77 1)

KTlN 11

VBE(Q1) = 7 Is,

where

(077 1)

K = Boltzmann's constant T = Temperature in degrees Kelvin q = Electroncharge

IS, = Reverse saturation current of Ql base-emitter junction

To utilize the output of the voltage regulator, a load, RL, must be connected between node V2 and ground....