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Precision Current Source Independent of Supply Voltage

IP.com Disclosure Number: IPCOM000094557D
Original Publication Date: 1965-Mar-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 28K

Publishing Venue

IBM

Related People

Ottesen, H: AUTHOR

Abstract

The circuit provides a plurality of constant currents I-C1...I-CN. Circuit 10 produces a constant reference current I-R. Zener diode 11 maintains a constant voltage across resistor 13. Hence, the emitter current for transistor T-A is held constant. Since the emitter current in T-A is constant, the collector current I-R is constant. Diode 14 compensates for variations in the base-emitter voltages of T-A due to temperature changes. Diode 14 is selected to have temperature characteristics which are similar to those of the base-emitter junction.

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Precision Current Source Independent of Supply Voltage

The circuit provides a plurality of constant currents I-C1...I-CN. Circuit 10 produces a constant reference current I-R. Zener diode 11 maintains a constant voltage across resistor 13. Hence, the emitter current for transistor T-A is held constant. Since the emitter current in T-A is constant, the collector current I-R is constant. Diode 14 compensates for variations in the base-emitter voltages of T- A due to temperature changes. Diode 14 is selected to have temperature characteristics which are similar to those of the base-emitter junction.

Since current I-R is held constant by circuit 10, the current through zener diode 21 is constant. Zener diode 21 maintains a constant voltage across resistors R-E1...R-EN. Due to the action of circuit 10, the voltage across diode 21 remains substantially constant even for a +/- 10% change in E. The constant voltage across resistors R-E1...R-EN forces constant emitter currents in transistors T-1 ...T-N. Since the emitter currents are constant, the collector currents I-C1...I-CN are also constant. Diodes 24 and 25 compensate for base- emitter junction variations and variations in the current gain due to temperature similar to the operation of diode 14.

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