An operating device for an illuminant , comprising: - a DC-DC switch-mode converter having at least one switch and an energy store , and - a controller that is configured to switch the at least one switch as a manipulated variable of a control loop , wherein a manipulated variable of the control loop is determined on the basis of a combination of a minimum current flow through the DC-DC switch-mode converter and a maximum current flow through the DC-DC switch-mode converter , wherein a controller of the control loop determines a difference between a reference variable and the manipulated variable and by suitable variation of the manipulated variable minimizes this difference, wherein a first switching time of the at least one switch is determined by a positive offset relative to the combination of the minimum current flow and the maximum current flow , wherein a second switching time of the at least one switch is determined by a negative offset relative to the combination of the minimum current flow and the maximum current flow , characterized in that the controller is configured to control in closed-loop control the operation of the switch-mode converter on the basis of a dimmer signal indicating a brightness desired by a user, the reference variable is determined on the basis of the dimmer signal , so that an average current flow to the illuminant is changed as a function of a desired dimmer level, and in addition the positive offset and/or the negative offset is changed as a function of the reference variable of the control loop , wherein the offsets are determined on the basis of a look-up table as a function of the reference variable of the control loop . - a DC-DC switch-mode converter having at least one switch and an energy store , and - a controller that is configured to switch the at least one switch as a manipulated variable of a control loop , wherein a manipulated variable of the control loop is determined on the basis of a combination of a minimum current flow through the DC-DC switch-mode converter and a maximum current flow through the DC-DC switch-mode converter , wherein a controller of the control loop determines a difference between a reference variable and the manipulated variable and by suitable variation of the manipulated variable minimizes this difference, wherein a first switching time of the at least one switch is determined by a positive offset relative to the combination of the minimum current flow and the maximum current flow , wherein a second switching time of the at least one switch is determined by a negative offset relative to the combination of the minimum current flow and the maximum current flow , characterized in that the controller is configured to control in closed-loop control the operation of the switch-mode converter on the basis of a dimmer signal indicating a brightness desired by a user, the reference variable is determined on the basis of the dimmer signal , so that an average current flow to the illuminant is changed as a function of a desired dimmer level, and in addition the positive offset and/or the negative offset is changed as a function of the reference variable of the control loop , wherein the offsets are determined on the basis of a look-up table as a function of the reference variable of the control loop . <EOS>