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# Variable Amplitude Constant Current Switch

IP.com Disclosure Number: IPCOM000098137D
Original Publication Date: 1960-Feb-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 26K

IBM

## Related People

Akmenkalns, IG: AUTHOR

## Abstract

The circuit is a constant current switch with adjustable amplitude control. The plot of the collector characteristic of a common base transistor amplifier shows that if a constant emitter current 1(E) is maintained, a load variation from Condition 1 (R(2)=O) to Condition 2 (R(2)=R(2) max.) can be permitted without variation in the collector current I(c).

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Variable Amplitude Constant Current Switch

The circuit is a constant current switch with adjustable amplitude control. The plot of the collector characteristic of a common base transistor amplifier shows that if a constant emitter current 1(E) is maintained, a load variation from Condition 1 (R(2)=O) to Condition 2 (R(2)=R(2) max.) can be permitted without variation in the collector current I(c).

A constant emitter current I(E) is maintained by providing a fixed voltage across R(1). As the base of transistor T(1) is driven more positive than V(1), the emitter voltage V(E1) is clamped to the collector voltage V(1). At this time transistor T(2) is conducting and its emitter voltage V(E2) is clamped to ground. Provided the input signal magnitude is V >=V(1), a fixed known voltage is established across R(1) and, therefore, a constant emitter current I(E) is maintained.

Since I(E) depends on V(EI) which in turn depends on V(1), control over V(1) provides adjustable collector current Ic. An alternate method of output current amplitude control is accomplished by controlling the value of R(1) for a fixed collector voltage V(1). The output current Ic is reduced to zero by returning the base of transistor T(1) to the reference potential.

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