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Current Limited Emitter Follower Circuit

IP.com Disclosure Number: IPCOM000095994D
Original Publication Date: 1964-Nov-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 27K

Publishing Venue

IBM

Related People

Di Gleria, PA: AUTHOR

Abstract

An emitter-follower circuit including transistor T1 forms part of a power supply and provides an output voltage on terminal 1. The value of this voltage is controlled by a control voltage applied to terminal 2.

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Current Limited Emitter Follower Circuit

An emitter-follower circuit including transistor T1 forms part of a power supply and provides an output voltage on terminal 1. The value of this voltage is controlled by a control voltage applied to terminal 2.

Under normal operating conditions, transistors T2 and T3 are saturated. The collector current of T1 is supplied through T2, diode D1 is reversely biased and T3 base current is supplied through resistor 3 and diode D2.

When an overload current is drawn from terminal 1, the T1 collector voltage falls until D1 conducts, turning T3 off. This causes the base potential of T2 to rise and this transistor turns off. Thus, T1 output current is drawn from the current applied to its base and the current through resistor 3. As resistor 1 has a value very much greater than resistors 4 and 5 the output current is considerably reduced.

When the fault causing the overload is rectified, the circuit returns to its normal operating condition.

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