An operating circuit for light-emitting means (18), in particular an LED string, contains an actively clocked power factor correction circuit (11), which produces a regulated output voltage (UBUS), by means of which the light-emitting means (18) are supplied directly or indirectly via at least one further converter stage (17). The regulation is performed by means of a control unit (16), which, as manipulated variable (tON), actuates clocking of a switch of the power factor correction circuit (11). The operating circuit is designed, in the event of the presence of a predefined event, for example a rapid or sudden change in the energy demand of the light-emitting means (18), selectively: —to change suddenly the value of the manipulated variable (tON) using feedforward control, and/or —to vary the time constant of the control loop of the output voltage (UBUS).