A control circuit for a switched-mode power supply having an input side (101) connectable to an electrical power source and an output side (102) connectable to a load. The control circuit comprises: a primary control circuit (140) adapted to generate a driving signal for a switching element (110) at the input side of the power supply; a secondary control circuit (150) adapted to monitor an output signal at the output side (102) of the power supply; and an opto-coupler (300, 400), wherein the opto-coupler is arranged to receive its input from the secondary control circuit and to provide a control signal to the primary control circuit, and the primary control circuit comprises a compensation circuit (900, 1000, 1100, 1400, 2010, 2610) adapted to process the control signal to generate a compensation signal for reducing power consumption in the opto-coupler, wherein the compensation circuit is adapted to generate the compensation signal such that a current in the opto-coupler tends to return to a desired minimum value.