A circuit (1202) for a resonant converter (1204; 1326), the resonant converter configured to operate in a burst mode of operation, the circuit configured to: receive a signal (1206; 1308) representative of the output of the resonant converter; compare the received signal (1206; 1308) representative of the output of the resonant converter with a reference signal (1208; 1304) in order to provide an error signal (1310); and process the error signal (1310) in order to provide a control signal (1210; 1328), wherein the control signal (1210; 1328) is configured to set the switching frequency of the resonant converter in order to control the output power during the on-time of a burst of the resonant converter.