Temperature setpoint circuit with hysteresis

Details Temperature setpoint circuit with hysteresis Temperature setpoint circuit with hysteresis

2006-03-06

2009-02-24

Nguyen, Matthew V (Department: 2838)

Electricity: power supply or regulation systems

Self-regulating

Using a three or more terminal semiconductive device as the...

C323S907000

Reexamination Certificate

active

07495426

ABSTRACT:
A temperature setpoint circuit comprises bipolar transistors Q1and Q2which receive currents I1and I2at their respective collectors and are operated at unequal current densities, with a resistance R1connected between their bases such that the difference in their base-emitter voltages (ΔVbe) appears across R1. An additional PTAT current I3is maintained in a constant ratio to I1and I2and provided to the collector of Q2while Q2is off, and is not provided while Q2is on. The circuit is arranged such that Q2is turned on and conducts a current equal to Ia when:ΔVbe=(kT/q)ln(NI1/Ia), where Ia=I2+I3, the temperature T at which ΔVbe=(kT/q)ln(NI1/Ia) being the circuit's setpoint temperature, such that the switching of current I3provides hysteresis for the setpoint temperature which is approximately constant over temperature.

REFERENCES:
patent: 5394078 (1995-02-01), Brokaw
patent: 5672961 (1997-09-01), Entrikin et al.
patent: 5821741 (1998-10-01), Brokaw
patent: 5828329 (1998-10-01), Burns
patent: 5982201 (1999-11-01), Brokaw et al.
Analog Devices, Inc., “Low Voltage, Resistor Programmable Thermostatic Switch”, AD22105, 1996, pp. 1-8.

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