Operating device for lighting means , - the operating device comprises - a switched resonant converter comprising at least two switches , and - a control unit configured to control the switching operation of the at least two switches by modulating a high frequency operation with low frequency PWM pulses with a varying frequency (Fpwm); wherein - the control unit 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); wherein - 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 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; and - the control unit is configured to keep the on-time duration (TON) of the PWM pulses constant at a minimum on-time duration (TONMIN) in the first power subrange (PSR1), and to keep the off-time duration (TOFF) between two PWM pulses constant at a minimum off-time duration (TOFFMIN) in the second power subrange (PSR2); wherein the minimum on-time duration (TONMIN) equals to the minimum off-time duration (TOFFMIN). - the operating device comprises - a switched resonant converter comprising at least two switches , and - a control unit configured to control the switching operation of the at least two switches by modulating a high frequency operation with low frequency PWM pulses with a varying frequency (Fpwm); wherein - a switched resonant converter comprising at least two switches , and - a control unit configured to control the switching operation of the at least two switches by modulating a high frequency operation with low frequency PWM pulses with a varying frequency (Fpwm); wherein - the control unit 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); wherein - 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 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; and - the control unit is configured to keep the on-time duration (TON) of the PWM pulses constant at a minimum on-time duration (TONMIN) in the first power subrange (PSR1), and to keep the off-time duration (TOFF) between two PWM pulses constant at a minimum off-time duration (TOFFMIN) in the second power subrange (PSR2); wherein the minimum on-time duration (TONMIN) equals to the minimum off-time duration (TOFFMIN). <EOS>