Mixed T_on-T_off modulation for a resonant converter

The present invention provides an operating device (1) for lighting means (10). The operating device (1) comprises a switched resonant converter comprising at least two switches (3a, 3b), and a control unit (4) configured to control the switching operation of the at least two switches (3a, 3b) by modulating a high frequency operation with low frequency PWM pulses with a varying frequency (Fpwm). The control unit (4) is configured to adjust an electrical power transferred by the switched resonant converter in a power range, the power range comprising at least a first power subrange (PSR1) and a second power subrange (PSR2) adjacent to the first power subrange (PSR1). The control unit is configured to decrease the electrical power transferred in the first power subrange (PSR1) by increasing the off-time duration (TOFF) between two PWM pulses, while the on-time duration (TON) of the PWM pulses is kept constant. The control unit (4) is configured to increase the electrical power transferred in the second power subrange (PSR2) by increasing the on-time duration (TON) of the PWM pulses, while the off-time duration (TOFF) between two PWM pulses is kept constant. In addition a luminaire and a method for operating one or more lighting means are provided.