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Resistive Current Source

IP.com Disclosure Number: IPCOM000081824D
Original Publication Date: 1974-Aug-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 22K

Publishing Venue

IBM

Related People

Gersbach, JE: AUTHOR

Abstract

This current source circuit minimizes sensitivity to power supply variations and is insensitive to base-emitter voltage variations.

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Resistive Current Source

This current source circuit minimizes sensitivity to power supply variations and is insensitive to base-emitter voltage variations.

The output current i(0) = +V+(R1/R2-1)V(be1) - V(be2) over R1 + R3 where V(be1) and V(be2) are the base-emitter voltages of transistors T1 and T2, respectively. When R1 = 2R2, the equation can be simplified to: i(0) = +V+V(be1) - V(be2) over R1 + R3.

The output current i(0) is then independent of the base-emitter voltage if transistors T1 and T2 track together and less dependent on the supply voltage +V since R1 becomes a relatively larger value when R2 is connected between the emitters of transistors T1 and T2. The above equations are valid only if at least .2 volt is produced across R3 in order to maintain equal currents in R3 and R4.

Other ratios of R1 to R2 vary the circuit so as to emulate a circuit having a number of series diode drops V(be) across the power supply of +V ranging from 2 to -infinity, which need not be integers.

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