| 摘要 |
The base of a thermal shutdown bipolar transistor having a VBE(on) which decreases with increasing temperature is biased with a bias voltage VPTATbias which increases proportionally with increasing absolute temperature. By supplying the base of the thermal shutdown transistor with a bias voltage VPTATbias 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 VPTATbias 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.
|
