A method for driving an electro-optical functional layer by a control, the functional layer being applied on a substrate and being variable in its transmissive and/or reflective properties by applying an electric field, the control unit having a supply voltage input and a feed output, and a voltage measuring system and an energy store, includes measuring a voltage actually available at the supply voltage input, if the available voltage is greater than a reference value, driving the functional layer with an AC voltage via the feed output, the energy store being charged at least in sections, if the available voltage is less than or equal to a reference value, driving the functional layer with a DC voltage via the feed output. At least part of the energy for the driving is drawn from the energy store. The DC voltage is less than the peak value of the AC voltage.