An active gain control circuit includes a dynamic voltage divider having a variable resistance configured to attenuate a rectified input line voltage to produce a reference signal, a filter-divider circuit configured to extract a DC-level attenuated reference voltage from the reference signal, and an operational amplifier configured to receive the DC-level attenuated reference voltage and a regulation voltage, and to generate a gate control signal based on a difference between the regulation voltage and the DC-level attenuated reference voltage, the variable resistance of the dynamic voltage divider being controlled by the gate control signal, and a comparison voltage generator configured to attenuate a comparison voltage to generate the regulation voltage.