An operating device for an illuminant comprising a LLC resonant converter including a LLC resonant circuit and at least one half bridge including a first transistor and a second transistor, wherein each transistor is configured to be controlled by a control signal; and a LC circuit arranged to generate the control signal, wherein the LC circuit comprises a first resonant circuit arranged to generate the control signal for the first transistor (T 1) and a second resonant circuit arranged to generate the control signal for the second transistor, wherein each of the first resonant circuit and the second resonant circuit comprises at least an inductor (L2a, L2b), a first capacitor (C2, C4) and a second capacitor (C3, C5), and the operating device comprises - a first switch for connecting the first capacitor in parallel with the second capacitor of the first resonant circuit, - a second switch for connecting the first capacitor in parallel with the second capacitor of the second resonant circuit, and control means configured to control the first switch to change the capacitance of the first resonant circuit and as a result the switching frequency of the first transistor and to control the second switch to change the capacitance of the second resonant circuit and as a result the switching frequency of the second transistor. a LLC resonant converter including a LLC resonant circuit and at least one half bridge including a first transistor and a second transistor, wherein each transistor is configured to be controlled by a control signal; and a LC circuit arranged to generate the control signal, wherein the LC circuit comprises a first resonant circuit arranged to generate the control signal for the first transistor (T 1) and a second resonant circuit arranged to generate the control signal for the second transistor, wherein each of the first resonant circuit and the second resonant circuit comprises at least an inductor (L2a, L2b), a first capacitor (C2, C4) and a second capacitor (C3, C5), and the operating device comprises - a first switch for connecting the first capacitor in parallel with the second capacitor of the first resonant circuit, - a second switch for connecting the first capacitor in parallel with the second capacitor of the second resonant circuit, and control means configured to control the first switch to change the capacitance of the first resonant circuit and as a result the switching frequency of the first transistor and to control the second switch to change the capacitance of the second resonant circuit and as a result the switching frequency of the second transistor. - a first switch for connecting the first capacitor in parallel with the second capacitor of the first resonant circuit, - a second switch for connecting the first capacitor in parallel with the second capacitor of the second resonant circuit, and control means configured to control the first switch to change the capacitance of the first resonant circuit and as a result the switching frequency of the first transistor and to control the second switch to change the capacitance of the second resonant circuit and as a result the switching frequency of the second transistor.