Device for controlling the current through a pn junction

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 (2a) connected to the voltage source (1), an output (2b) and a control input (2c), thereafter a measurement resistor (3), which is connected to the output (2b) of the current generator (2), and finally a controlled output (4a), to which the PN junction (4) is connected, where the device furthermore comprises a control signal input (6b), 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 (5c) of the differential amplifier (5), the integrating device (6) is arranged to, on its output (6c), 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 (2b) 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 (2a) and its control input (2c), and in that the reference voltage of the integrating device (6) is constituted of the voltage of the voltage source (1).