Browse Prior Art Database

Wide Current Range Low Voltage Limiter

IP.com Disclosure Number: IPCOM000035310D
Original Publication Date: 1989-Jul-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 24K

Publishing Venue

IBM

Related People

Martin, J: AUTHOR [+2]

Abstract

A simple circuit providing a constant low voltage drop for a wide current range is described. The invention uses the association of two usual silicon diodes and a transistor.

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Wide Current Range Low Voltage Limiter

A simple circuit providing a constant low voltage drop for a wide current range is described. The invention uses the association of two usual silicon diodes and a transistor.

In some applications, it is necessary to have a device that creates a low voltage drop, as constant as possible, for a wide current range.

This can be the case for telephone handset switch-hook detector, where the described device is put in parallel with the detector in order to limit the current flow into the detector inputs.

In that case, the requested clamping voltage is around 1.9 volts, and PTT national requirements are difficult to fulfill in that respect with usual silicon diodes.

The more usual solution is to put 3 diodes in series. It works correctly for low currents. Unfortunately, for larger currents, VD is too important. The proposed invention uses one base emitter junction of a transistor.

One portion of the current flowing through D1/D2 is used to polarize the base emitter junction of T. Then, the current that transistor T is able to drive is IB multiplied by the transistor gain; thus, it is the main part of IT. It means that the current flowing through D1 and D2 remains low and maintains a low voltage drop through D1 and D2.

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