Abstract: A power supply apparatus for supplying a device (1) with electric energy comprises at least two test inputs (5a, . . . , 5d) for receiving test signals which are dependent on a variable which itself is dependent on the power applied to the device. Each test input is connected to a first input of an associated comparator circuit (9a, . . . , 9d), the second input (11a, . . . , 11d) of which is connected to a generator for generating a number of reference signals which corresponds to the number of test inputs. The reference signals represent the desired values of said variables. The outputs of the comparator circuits are connected to a control member which is adapted to control the power applied to the device by the power supply apparatus so that at least one of the variables is essentially equal to the desired value, the other variables deviating from their desired values in a predetermined sense only.

Abstract: A circuit comprising a semiconductor photodiode with a first and a second terminal and an internal series resistor, including an amplifier with a first input, a second input and an output, the first photodiode terminal being connected to the first amplifier input, the second photodiode terminal being connected to the second amplifier input and a negative feedback being inserted between the output of the amplifier and its first input, characterized in that a coupling is introduced between the output and the second input of the amplifier, by means of which a voltage is generated between the second input of the amplifier and the second terminal of the photodiode, this voltage being oppositely equal to the product of the internal series resistance and the signal current flowing through the resistor.