Patent ID: 6909275

Claim:
An electrical circuit for driving a load, comprising a transistor having a load current flowing therethrough, a measurement device for determining the voltage drop across the transistor, a device for impressing a measuring current into the transistor, and a device for determining the resistance value of the transistor in its ON state, this resistance value being between a known maximum value (R XMAX ) and a known minimum value (R XMIN ), wherein the device for determining the resistance value is provided with a measuring bridge having the transistor and a known reference resistor arranged in its first bridge arm and having three respectively known resistors arranged in its second bridge arm, the first bridge arm comprising a resistor connecting point between the reference resistor and the transistor, and the second bridge leg comprising a first resistor connecting point (K 2 ) between the first resistor connected to the transistor, and the second resistor, as well as a second resistor connecting point between the second resistor and the third resistor connected to the reference resistor, and the values of the reference resistor of the first bridge arm and of the three resistors of the second bridge arm being selected in such a manner that (i) the potential of the resistor connecting point of the first bridge leg is equal to the potential of the first resistor connecting point of the second bridge leg if the transistor is at its minimum resistance value, and (ii) the potential of the resistor connecting point of the first bridge leg is equal to the potential of the second resistor connecting point of the second bridge leg if the transistor is at its maximum resistance value.