1. A driver circuit for delivering a current to a load, comprising:an input for receiving an input voltage, comprising first and second terminals;
a driver unit for providing a current for the load from the input voltage, wherein the driver unit comprises a linear driver which comprises a current regulating element (Q3) in series between the input and the load, said current regulating element having a controllable resistive characteristic, an operating current level for the load being controlled by a driver input voltage controlling a resistance of the current regulating element;
a compensation unit in series with the driver unit and the input, for providing a compensating voltage thereby to control the voltage across the driver unit in dependence on the input voltage and operating conditions of the load;
wherein the compensation unit comprises a switch mode power converter and a second capacitor (C2) as an energy source of the switch mode power converter, with the current regulating element (Q3), the load and the second capacitor (C2) in series connection between the first and second terminals, wherein
the second capacitor (C2) is disposed at the output of the load and is adapted to be charged by a portion of the current from said input voltage that has flowed through the current regulating element (Q3) and the load;
wherein the driver input voltage controls a base current of a first transistor coupled to the current regulating element; and
wherein the first transistor controls a collector current of a second transistor coupled to the current regulating element.