Power supply with multi-parameter control

A power supply apparatus for supplying electric energy to a device with multiple variables, said power supply apparatus comprising:

• a number of test inputs for receiving respective test signals from the device wherein at least one of said test signals is dependent on a device variable which itself is dependent on the power applied to the device,
• a reference signal generator which generates a number of reference signals which corresponds to the number of test inputs, said reference signals being a measure of desired values of the device variables,
• a number of comparator circuits corresponding to the number of test inputs, each comparator circuit having a first and second input,
• means coupling the first inputs of the comparator circuits to respective test inputs,
• second means coupling the second inputs of the comparator circuits to the reference signal generator so as to receive therefrom respective reference signals,
• a control member having input means coupled to outputs of the comparator circuits, said control member being operative to control the power applied to the device by the power supply apparatus so that at least one of the variables corresponding to one of the test signals is equal to the desired value of said one variable, and wherein the control member controls other variables corresponding to other test signals so that they deviate from their respective desired values in a predetermined sense.