A filter circuit comprising a first feedback circuit configured to: receive a sensed-voltage-level-signal representative of a sensed voltage across a current sensing element receive a voltage-set-point-signal; and set a regulation-control-signal for a current regulation device such that the sensed-voltage-level-signal tends towards the voltage-set-point-signal. The filter circuit also comprises a second feedback circuit configured to: receive a predetermined-threshold-signal; and receive a regulation-control-voltage-signal, representative of a voltage level of the regulation-control-signal. The second feedback circuit is configured to adjust the voltage-set-point-signal in accordance with a comparison between the regulation-control-voltage-signal and the predetermined-threshold-signal.