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Voltage and Temperature Insensitive Current Source

IP.com Disclosure Number: IPCOM000078417D
Original Publication Date: 1973-Jan-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 2 page(s) / 27K

Publishing Venue

IBM

Related People

DeBrita, AA: AUTHOR [+2]

Abstract

The circuit provides a controlled DC voltage at its output. Specifically, the circuit operates as follows: Transistors T4 and T5 and resistors R5, R6 and R7 are arranged in a network such that the voltage across R5 and R7 is relatively invariant, except for changes in the supply voltage or shifts in base-emitter voltage of transistors T4 and T5 due to temperature. Thus a fixed collector current flows in T4. Transistor T5 acts as an emitter-follower driving transistors T4 and T3, but not drawing a significant current through R7. Because transistor T3 and resistor R4 are connected across transistor T4 and resistor R5 the collector currents of both transistors track, while resistors R4 and R5 help in insuring that the base-emitter voltage variations in transistors T4 and T5 are reduced.

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Voltage and Temperature Insensitive Current Source

The circuit provides a controlled DC voltage at its output. Specifically, the circuit operates as follows: Transistors T4 and T5 and resistors R5, R6 and R7 are arranged in a network such that the voltage across R5 and R7 is relatively invariant, except for changes in the supply voltage or shifts in base-emitter voltage of transistors T4 and T5 due to temperature. Thus a fixed collector current flows in T4. Transistor T5 acts as an emitter-follower driving transistors T4 and T3, but not drawing a significant current through R7. Because transistor T3 and resistor R4 are connected across transistor T4 and resistor R5 the collector currents of both transistors track, while resistors R4 and R5 help in insuring that the base-emitter voltage variations in transistors T4 and T5 are reduced. The resistors R3 and R7 being approximately the same value, causes any change in the negative voltage supply to change the current in these resistors by the same amount. Thus changes in current in resistor R3 are absorbed by the collector changes in transistor T3, so that the collector current in transistor T2 remains relatively constant. Any shifts in the base-emitter voltage of the transistor T2 due to temperature changes also appear across resistors R3 and R7.

In this way variations of the negative voltage supply or temperature causes minimal change in potential across the output, thereby causing low variation in collector current...