Resistor programmable temperature switch

DETAILED DESCRIPTION What is claimed is: 1.
A resistor programmable temperature switch for indicating that a preselected trip temperature has been reached, comprising: first and second bipolar transistors of like polarity having a fixed ratio of emitter areas; means for connecting the emitters of said first and second transistors to a common terminal; first and second current sources for providing first and second predetermined currents to the collectors of said first and second transistors, respectively; a third transistor having means for connecting its control terminal to said first current source and a first load terminal connected to the base of said first transistor for operating said first transistor to conduct said first predetermined current from said current source; means for interconnecting a second load terminal of said third transistor with a power supply terminal; a resistor network including first and second resistors connected between the base of said first transistor and said common terminal for biasing the base of said second transistor to a fraction of the base emitter voltage of said first transistor; a fourth transistor having means for connecting a first load terminal of said fourth transistor to said common terminal and means for connecting the control terminal of said fourth transistor to said second current source; the load current of said fourth transistor changing state when the preselected trip temperature has been reached.
2.
The resistor programmable temperature switch of claim 1 in which said first resistor includes a first trimmable resistance for correcting for sheet resistance errors and current density errors incurred in manufacturing of said first and second transistors.
3.
The resistor programmable temperature switch of claim 1 in which said second resistor includes a second trimmable resistance for correcting for sheet resistance errors in said second trimmable resistance and for compensating for manufacturing variations in the base-emitter voltages of said first and second transistors