Method for electrically controlling a functional element enclosed in a glazing unit

A method for electrically controlling at least one functional element with electrically controllable optical properties enclosed in a glazing unit, the method comprising:

• controlling the optical properties by a control unit, wherein the control unit is connected to at least two transparent flat electrodes of the at least one functional element,
• applying an electrical voltage by the control unit between the at least two flat electrodes and periodically changing a polarity of the voltage,
• wherein the electrical voltage has a trapezoidal profile, and wherein by the control unit
• a) an increasing electrical voltage is applied for charging the at least one functional element, wherein the electrical voltage increases to a first peak value,
• b) the electrical voltage is reduced from the first peak value to a final voltage for discharging the at least one functional element,
• c) the at least one functional element is charged with the increasing electrical voltage with reversed polarity as in step a), wherein the electrical voltage increases to a second peak value,
• d) the electrical voltage is reduced from the second peak value to the final voltage for discharging the at least one functional element, and
• the steps a) through d) are repeated periodically, and
• wherein the control unit has an accumulator for temporary energy storage and wherein in step b) and/or in step d) electrical energy is transferred from the at least one functional element to the control unit and the control unit stores energy transferred from the at least one functional element temporarily in said accumulator;
• wherein the control unit includes a switching device comprising a first half-bridge circuit connected to a first of the flat electrodes and a second half-bridge circuit connected to a second of the flat electrodes, each half-bridge circuit being connected to the respective flat electrode by an LC filter including (1) a capacitor connected having a first plate connected to the respective flat electrode and a second plate connected to a ground potential and (2) an inductor coil having a first end connected to the first plate of the capacitor and the respective flat electrode;
• the first half-bridge circuit further comprising a switching transistor and the accumulator, one terminal of the accumulator being connected to a second end of the inductor of the first half-bridge circuit, the switching transistor having one terminal connected to the ground potential and another terminal connected to the second end of the inductor of the first half-bridge circuit;
• wherein the switching transistor switches between (1) an off state ceasing current flow to the ground potential therethrough to cause current flowing from the second end of the inductor to charge the accumulator and (2) an on state connecting the second end of the inductor to the ground potential;
• wherein a pulse width modulator is used during said discharging of step b) and/or in step d) to switch the switching transistor in accordance with a duty cycle, including to said off state to cause current flowing from the second end of the inductor to charge the accumulator and thus store energy transferred from the at least one functional element temporarily in said accumulator.