A DC current regulator circuit comprises a first circuit node (32) which is operable to receive an external input voltage. A transistor (M1) has an input, a first leg and a second leg. The first leg of the transistor is isolated from the first circuit node (32). An amplifier (10) has an output connected to the input of the transistor (M1), a first amplifier input for receiving a reference voltage (V.sub.REF) and a second amplifier input connected to the first circuit node (32). A low-pass filter (33) connects between the output of the amplifier and the first circuit node (32). A current mirror (36) connects in series with the second leg of the transistor (M1) and has a first branch (38) for providing a regulated output current and a second branch (37) which connects to the first circuit node (32). The current regulator has reduced sensitivity to conducted EMI received at the first circuit node (32).