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Browse Prior Art Database

Reflective Current Source

IP.com Disclosure Number: IPCOM000122333D
Original Publication Date: 1991-Nov-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 1 page(s) / 33K

Publishing Venue

IBM

Related People

Banker, DC: AUTHOR [+4]

Abstract

Historically, positive current sources have been extremely difficult to build in bipolar due to the lack of a vertical (high current capability) PNP. This circuit circumvents this problem and also allows negative current sources (sinks) to be derived (reflected) from it.

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This is the abbreviated version, containing approximately 100% of the total text.

Reflective Current Source

      Historically, positive current sources have been extremely
difficult to build in bipolar due to the lack of a vertical (high
current capability) PNP.  This circuit circumvents this problem and
also allows negative current sources (sinks) to be derived
(reflected) from it.

      Resistor R1, transistor T1, and Vref provide the primary
control for this current source.  T1 provides base drive for T3 and
the emitter current for T2 (Ict1 = Iet2 + Ibt3).  T2 and R2 provide
the bias voltage for T3 which is used as the driving element for the
output current.

      Since Iet3 >> Ict1 the operating conditions of T1 are not
affected by the high output current requirements, and because Iet2 >>
Ibt3, the T2/R2 network provides regulation for Ibt3.  This
configuration allows for the use of lamp LPNP with low Beta operating
at very small currents.  The tolerance of this circuit is determined
primarily by the characteristics of T1, R1, and Vref.

      Disclosed anonymously.