A control circuit varies the power of a load powered by an alternating voltage, comprising: a first thyristor and a first diode connected in antiparallel between first and second nodes, the cathode of the first diode being on the side of the first node; a second thyristor and a second diode connected in antiparallel between the second node and a third node, the cathode of the second diode being on the side of the third node; third and fourth diodes connected in antiseries between the first and third nodes, the cathodes of the third and fourth diodes being connected to a fourth node; a transistor between the second and fourth nodes; and a control unit for controlling the first and second thyristors and the transistor.