Patent ID: 7911157

Claim:
Device for controlling the current through a PN junction ( 4 ) comprising a voltage source ( 1 ) connected in series to, in order, firstly a controllable current generator ( 2 ), comprising an input ( 2 a ) connected to the voltage source ( 1 ), an output ( 2 b ) and a control input ( 2 c ), thereafter a measurement resistor ( 3 ), which is connected to the output ( 2 b ) of the current generator ( 2 ), and finally a controlled output ( 4 a ), to which the PN junction ( 4 ) is connected, where the device furthermore comprises a control signal input ( 6 b ), arranged to receive a desired value control signal in the form of a voltage, where the device also comprises a differential amplifier ( 5 ) and an integrating device ( 6 ), where the differential amplifier ( 5 ) is arranged to measure the voltage drop across the measurement resistor ( 3 ) and to apply this voltage drop in amplified form on the output ( 5 c ) of the differential amplifier ( 5 ), the integrating device ( 6 ) is arranged to, on its output ( 6 c ), apply a voltage which is the integrated difference between the output voltage of the differential amplifier ( 5 ) and the desired value control signal, the output voltage of the integrating device ( 6 ) is arranged to constitute control signal to the current generator ( 2 ), which on its output ( 2 b ) is arranged to give rise to a current which depends on the voltage supplied from the voltage source ( 1 ) and the control voltage from the integrating device ( 6 ), characterized in that the integrating device ( 6 ) comprises a balanced integrator, in that the current through the output of the controllable current generator ( 2 ) is proportional to the voltage difference between its input ( 2 a ) and its control input ( 2 c ), and in that the reference voltage of the integrating device ( 6 ) is constituted of the voltage of the voltage source ( 1 ).