Breakpoint compensation and thermal limit circuit
AssigneeLinear Technology Corporation
InventorCarl T. Nelson
Life of this patent
Estimating the term…
Abstract
A voltage reference circuit including a Brokaw Cell band-gap reference circuit is provided with breakpoint compensation to adjust the temperature coefficient of the reference voltage provided by the Brokaw Cell as a function of temperature. The voltage reference circuit also includes a thermal limit transistor which is biased by a voltage having a positive temperature coefficient. The thermal limit transistor draws a rapidly increasing current when the operating temperature reaches a predetermined value.
Claims22
ln a voltage reference circuit having an output terminal for providing an output voltage at an operating temperature within a range of operating temperatures, first and second supply terminals and a band gap voltage reference providing at a first node a reference voltage which varies in accordance with a temperature coefficient, and at a second node a voltage which is proportional to the difference between base-emitter voltages of two transistors and which has a positive temperature coefficient, a breakpoint compensation circuit comprising:
- first resistive means connected between the output terminal and the first node;
- means connected to the output terminal and the first supply terminal for supplying a current to the output terminal;
- and
- compensating means connected to the first node, the second node and the second supply terminal, and responsive to the voltage at the second node, for developing a compensating voltage across said first resistive means when the operating temperature reaches a breakpoint compensation threshold whereby the output voltage is the sum of the reference voltage and the compensating voltage, and exceeds the reference voltage at operating temperatures equal to or greater than the breakpoint threshold temperature.
In a voltage reference circuit having an output terminal for providing an output voltage at an operating temperature within a range of operating temperatures, first and second supply terminals and a band gap voltage reference providing at a first node a reference voltage which varies in accordance with a temperature coefficient, and at a second node a voltage which is proportional to the difference between base-emitter voltages of two transistors and which has a positive temperature coefficient, a breakpoint compensation circuit comprising:
- a first resistor connected between the output terminal and the first node;
- means connected to the first supply terminal and the output terminal for supplying a current to the output terminal;
- a transistor;
- and
- a second resistor connected at one end to the second supply terminal;
- wherein:
- said transistor has a base connected to the second node, a collector connected to the first node and an emitter connected to another end of said second resistor to define a third node, said transistor functioning to provide breakpoint temperature compensation by producing a compensating voltage drop across said first resistor when the operating temperature reaches a breakpoint threshold temperature, such that the output voltage is the sum of the reference voltage and the compensating voltage and exceeds the reference voltage at temperatures equal to or greater than the breakpoint threshold temperature.
In a circuit having an output terminal for providing an output voltage at an operating temperature within a range of operating temperatures and a band gap voltage reference providing at a first node a first voltage which has a temperature coefficient, and at a second node a second voltage which is proportional to the difference between base-emitter voltages of two transistors and which has a positive temperature coefficient, a breakpoint compensation circuit comprising:
- means for supplying a current to the output terminal;
- and
- means connected to the output terminal and to the first node, and responsive to the second voltage at the second node, for developing a compensating voltage between the output terminal and the first node when the operating temperature reaches a breakpoint compensation threshold, whereby the output voltage is comprised of at least the sum of the first and compensating voltages, and exceeds the first voltage at operating temperatures which exceed the breakpoint threshold temperature.
In a circuit having an output terminal for providing an output voltage at an operating temperature within a range of operating tempertures and a band gap voltage reference providing at a first node a first voltage which has a temperature coefficient, and at a second node a second voltage which is proportional to the difference between base-emitter voltages of two transistors and which has a positive temperature coefficient, a thermal shutdown circuit comprising:
- means responsive to the second voltage at the second node for producing at a third node a third voltage having a positive temperature coefficient greater than that of the second voltage;
- and
- means responsive to the voltage at the third node for producing a thermal shutdown signal having an effective positive temperature coefficient equal to or greater than 6 mV/.degree.C.
In a circuit having an output terminal for producing an output voltage at an operating temperature within a range of operating temperatures and a supply terminal and a band gap voltage reference providing at a first node a first voltage which has a temperature coefficient, and at a second node a second voltage which is proportional to the difference between base-emitter voltages of two transistors and which has a positive temperature coefficient, a thermal shutdown circuit comprising:
- a resistor connected at one end to the supply terminal;
- a transistor having a base connected to the second node, a collector connected to the first node and an emitter connected to another end of said resistor to define a third node;
- and
- a second transistor having a base connected to the third node and an emitter connected to the supply terminal, whereby said second transistor is biased by a voltage having an effective positive temperature coefficient equal to or greater than 6 mV/.degree.C.
Dependencies are inferred from the claim text.