Patent ID: 7461974

Claim:
A method for determining the temperature of a bipolar junction transistor, which has an emitter terminal that carries an emitter current Ie, a base terminal that carries a base current Ib, and a collector terminal that carries a collector current Ic, and wherein said currents are related by Ie=Ib+Ic, the method comprising the steps of: applying a first emitter current (Ie 1 ) to the emitter terminal of said transistor, wherein said first emitter current (Ie 1 ) comprises a first base current component (Ib 1 ) and a first collector current component (Ic 1 ) with the relationship Ie 1 =Ib 1 +Ic 1 , adjusting the first emitter current (Ie 1 ) while sensing the first base current (Ib 1 ) at the base terminal until a sensed first base current (Ib 1 ) is substantially equal to a different between the adjusted first emitter current (Ie 1 ) and a first predetermined target collector current (ICT 1 ), sensing a first voltage (Vbe 1 ) between the base and emitter terminals of said transistor while said adjusted first emitter current (Ie 1 ) is applied to said emitter terminal, applying a second emitter current (Ie 2 ) to the emitter terminal of said transistor, wherein said second emitter current (Ie 2 ) comprises a second base current component (Ib 2 ) and a second collector current component (Ic 2 ) with the relationship Ie 2 =Ib 2 +Ic 2 , adjusting the second emitter current (Ie 2 ) while sensing the second base current (Ib 2 ) at the base terminal until a sensed second base current (Ib 2 ) is substantially equal to a difference between the adjusted second emitter current (Ie 2 ) and a second predetermined target collector current (ICT 2 ), with the first and second target collector currents (ICT 1 , ICT 2 ) differing in magnitude, sensing a second voltage (Vbe 2 ) between the base and emitter terminals of said transistor while said adjusted second emitter current (Ie 2 ) is applied to said emitter terminal, and determining the temperature of said transistor based, at least in part, on a difference between said first and second voltages (Vbe 1 and Vbe 2 ).