An operating device for an illuminant, comprising: - a DC-DC switch-mode converter having at least one switch (111, 112, 211, 211, 212) and an energy store (102, 202), and - a controller that is configured to switch the at least one switch (111, 112, 211, 212) 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 (315, 316) 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 (111, 112, 211, 211, 212) and an energy store (102, 202), and - a controller that is configured to switch the at least one switch (111, 112, 211, 212) 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 (315, 316) are determined on the basis of a look-up table as a function of the reference variable of the control loop.