Patent ID: 8446203

Claim:
A low side clamping circuit having a control portion, a sense portion, and a bipolar clamp transistor, the circuit comprising: a first current source for generating a first current for setting a clamp voltage; a second current source for generating a second current through the control portion; an NPN bipolar first transistor in the sense portion having its collector coupled to a positive power supply voltage, wherein a voltage at its emitter substantially follows a voltage at its base; an NPN bipolar second transistor in the control portion having its collector coupled to the second current source, its emitter coupled to a base of the clamp transistor, and its base coupled to the base of the first transistor; an NPN bipolar third transistor in the control portion having its base coupled to the first current source, its collector coupled to the base of the clamp transistor, and its emitter coupled to ground; an NPN bipolar fourth transistor in the sense portion having its collector coupled to the emitter of the first bipolar transistor, its base coupled to the collector of the third transistor and to the base of the clamp transistor, and its emitter coupled to an emitter of the clamp transistor; a first resistive element coupled in series between the first current source and the collector of the fourth transistor, wherein, upon the first current source generating the first current, a first voltage is generated at the base of the fourth transistor, wherein the fourth transistor turns on when a voltage approximately equal to the clamp voltage is applied to an emitter of the fourth transistor, and wherein the clamp transistor turns on when the fourth transistor turns on to clamp the emitter of the clamp transistor at approximately the clamp voltage.