Thermal shutdown circuit using a pair of scaled transistors

Details Thermal shutdown circuit using a pair of scaled transistors Thermal shutdown circuit using a pair of scaled transistors

1994-09-27

1998-04-07

Gaffin, Jeffrey A.

Electricity: electrical systems and devices

Safety and protection of systems and devices

Circuit interruption by thermal sensing

361106, 361 57, 361 98, 361 71, H02H 504

Patent

active

057371709

ABSTRACT:
The base of a thermal shutdown bipolar transistor having a V.sub.BE(on) which decreases with increasing temperature is biased with a bias voltage V.sub.PTATbias which increases proportionally with increasing absolute temperature. By supplying the base of the thermal shutdown transistor with a bias voltage V.sub.PTATbias which increases with increasing temperature rather than a bias voltage that remains constant or decreases with increasing temperature, the temperature at which the thermal shutdown transistor turns on is made more predictable and the thermal shutdown transistor is made to turn on more sharply at a desired thermal shutdown temperature. The bias voltage V.sub.PTATbias may be generated by driving a current which increases proportionally with increasing absolute temperature across a resistor. Current sources employing feedback control loops are disclosed for generating such a current. Startup current sources are disclosed for starting control loop operation. A hysteresis circuit is disclosed which causes the thermal shutdown transistor to turn on at a relatively high temperature and to turn off at a relatively low temperature.

REFERENCES:
patent: 4092693 (1978-05-01), Ishikawa et al.
patent: 4574205 (1986-03-01), Nagano
patent: 4958122 (1990-09-01), Main
patent: 5266885 (1993-11-01), Brambilla et al.

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