A method and circuit for supplying a variable voltage to an electrical a.c. load (R, L), comprising: a control signal input for receiving a switching control signal to control load output voltage; first and second circuit output terminals (ACL1, ACL2) for connection to the load; first switch means (S1) having an input coupled to the control signal input and having an output coupled between one (ACL1) of the circuit output terminals (ACL1) and a first a.c. line terminal (AC1); second switch means (S2) having an input coupled to the first switch means and having an output coupled between the first and second circuit output terminals (ACL1, ACL2) and coupled to a second a.c. line terminal (AC2); and providing a switching control signal to the control signal input to switch the first and second switch means complementarily. The switch means may each comprise a power transistor (Q1; Q2) and a bridge rectifier (B1; B2).