The invention provides a retrofit LED lamp driver having a shunt switch to alternately shunt (for a first duration) and not shunt (for a second duration) received AC power. The first duration is concurring with a first polarity of each AC cycle of the AC power, for a first period comprising at least one AC cycle, and the first duration is concurring in a second, opposite polarity of the AC power, for a second period comprising another at least one AC cycle not overlapping with the first duration. Alternating the first and second periods are provided. Any DC offset in the current drawn caused by the shunting operation is thereby cancelled over time.