Protective circuit having enhanced thermal shutdown

Details Protective circuit having enhanced thermal shutdown Protective circuit having enhanced thermal shutdown

1994-08-25

1995-09-05

Wambach, Margaret Rose

Miscellaneous active electrical nonlinear devices, circuits, and

External effect

Temperature

327 83, 327262, 327378, H03K 5153, H03H 1126

Patent

active

054481740

ABSTRACT:
A protective circuit having enhanced and accurate thermal shutdown temperatures. The protective circuit establishes the thermal shutdown temperature within a predetermined range and provides an output signal when the thermal shutdown temperature is exceeded. The protective circuit, in one embodiment, comprises a current generator for supplying a predetermined collector current I.sub.c1, a current mirror arrangement for supplying a collector current I.sub.c2 which has a mirror response to that of the collector current I.sub.c1, a resistor arranged to have the mirror collector current I.sub.c2 flowing therethrough, and the combination of a resistor and a bipolar transistor serving as a thermal sensor. The current generator comprises at least a pair of bipolar transistors selected from one of the NPN and PNP types with each of said pair operating with different current densities. The base electrodes of the pair are interconnected by a resistor. The collector current I.sub.c1 flows through another resistor connected to the emitter electrode of one of said bipolar transistors. The current mirror arrangement has its mirror collector current determined by the value of the resistor at the emitter electrode of the bipolar transistor. The current mirror arrangement comprises bipolar transistors selected to be of the opposite NPN and PNP types as the current generator. The bipolar transistor serving as the thermal sensor is selected to be of the same type NPN and PNP as the current generator and has a known beta (.beta.) vs. V.sub.be relationship. The bipolar transistor is arranged in the output stage of the protective circuit and establishes a quantity V.sub.tsd which determines the thermal shutdown temperature. The V.sub.tsd quantity tracks the response of the beta (.beta.) parameter so as to cancel the effects that the variable V.sub.be parameter contributes to the thermal shutdown temperature.

REFERENCES:
patent: 4034241 (1977-07-01), van der Burg et al.
patent: 4401898 (1983-08-01), Sommerer
patent: 4760286 (1988-07-01), Pigott
patent: 4945260 (1990-07-01), Naghshineh et al.
patent: 5077491 (1991-12-01), Heck et al.
patent: 5359236 (1994-10-01), Giordano et al.

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