Browse Prior Art Database

Monolithic Thermal Protection Circuit

IP.com Disclosure Number: IPCOM000083709D
Original Publication Date: 1975-Jul-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

Chang, CS: AUTHOR

Abstract

This is a temperature sensing circuit which can be fabricated totally within a semiconductor substrate, for thermal protection of devices on the same substrate or on other, related substrates or modules. It is preferably used to trigger externally located thermal protection devices.

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Monolithic Thermal Protection Circuit

This is a temperature sensing circuit which can be fabricated totally within a semiconductor substrate, for thermal protection of devices on the same substrate or on other, related substrates or modules. It is preferably used to trigger externally located thermal protection devices.

The circuit shown is insensitive to absolute device parameters; rather it utilizes the excellent adjacent device parameter tracking characteristics, which are typical of integrated circuit structures. Thermal sensing depends upon the negative temperature coefficient of VBE and its inverse relationship to the log of IE.

When the temperature increases, device Q3B is turned "on" by the output from group 1 while Q3A is turned "off". When the temperature decreases, Q3A is turned on by the output from group 2 while Q3B is turned off. This switching action of the current switch differential amplifier produces a 1 or 0 at the output of the emitter-follower Q4. Critical temperature control can be achieved by placing an external variable resistor in series with RL2.

The number of transistors Q1B may vary, with better sensitivity being realized when more transistors are put in parallel. Excellent tracking of the VBE characteristic is needed for Q1A and Q1B and for Q2A and Q2B. Good tracking only is needed between Q3A and Q3B. Excellent resistor tracking is required among RS1, RL1, RS2, RL2, RE1 and RE2.

The components RL1, RE1, RS2 and RE2 are selected so th...