Thermal shutdown circuit using a pair of scaled transistors
US5737170A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Sep 27, 1994 |
| Grant date | Apr 7, 1998 |
| Priority date | — |
| Expiry date | Sep 27, 2014 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH02H5/044
- WIPO fieldElectrical machinery, apparatus, energy
- WIPO sectorElectrical engineering
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.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.