Circuit apparatus for controlling a glazing unit whose transparency is switchable, and switchable glazing assembly, motor vehicle and method for controlling a glazing unit whose transparency is switchable

1. A circuit apparatus for controlling a glazing unit whose transparency is switchable, the circuit apparatus comprising:

a potential-isolated circuit part which, in order to set a predefined transparency state on the glazing unit, is configured to generate a periodically alternating drive voltage with a predetermined first period duration, wherein a voltage source is provided, to which the potential-isolated circuit part is connected via a transformer and configured to operate the transformer with an AC voltage, the AC voltage having a second period duration shorter than the first period duration, wherein the potential-isolated circuit part is configured to receive a transformed AC voltage from the transformer and, in repeatedly alternating switching phases, to respectively forward only positive half-cycles of the transformed AC voltage to an electrical capacitance of the glazing unit in the first switching phase and to forward only negative half-cycles of the transformed AC voltage to the electrical capacitance of the glazing unit in the subsequent, second switching phase utilizing a converter device controlled by a control device, wherein a duration of two successive switching phases corresponds to the first period duration.

2. The circuit apparatus as claimed in claim 1 , wherein the drive voltage is free of DC voltage and a connection of the transformer is permanently connected to a connection of the glazing unit during the switching phases.

3. The circuit apparatus as claimed in claim 1 , wherein the control device is configured to vary a drive frequency corresponding to the first period duration by at least one of changing a generator frequency of the voltage source that corresponds to the second period duration, changing a number of half-cycles for each switching phase, and changing an amplitude of the AC voltage of the voltage source.

4. The circuit apparatus as claimed in claim 1 , wherein the control device is configured, utilizing a voltage correction, to set an amplitude of the AC voltage of the voltage source on the basis of active power losses which are produced by a leakage resistor of the glazing unit.

5. The circuit apparatus as claimed in claim 4 , wherein, to determine the active power losses, the control device is configured to determine a current intensity value of a resulting electrical current during the forwarding of at least one half-cycle and to set the amplitude on the basis of the current intensity value by means of a predetermined assignment rule.

6. The circuit apparatus as claimed in claim 1 , wherein at least one of a series circuit comprising at least two switchable glazing units and a parallel circuit comprising at least two switchable glazing units is connected to the potential-isolated circuit part.

7. The circuit apparatus as claimed in claim 1 , wherein at least one further potential-isolated circuit part is connected to the transformer for the purpose of respectively connecting a further switchable glazing unit, and the control device is configured to switch the switching phases of the converter device and the switching phases of a respective further converter device of the at least one further potential-isolated circuit part in a phase-shifted manner.

8. The circuit apparatus as claimed in claim 1 , wherein a polarity reversal rate between the first switching phase and the second switching phase corresponds to a resonant frequency formed by the capacitance of the switchable glazing unit and an inductance of the transformer.

9. The circuit apparatus as claimed in claim 1 , wherein the control device is configured to respectively change over between the switching phases when the transformed AC voltage changes between two opposite half-cycles, with the result that the drive voltage has a profile with sinusoidal edges.

10. The circuit apparatus as claimed in claim 9 , wherein a drive frequency corresponding to the first period duration is greater than a cut-off frequency at which a flickering effect of the switchable glazing unit would result, but is less than 10 times the cut-off frequency.

11. The circuit apparatus as claimed in claim 1 , wherein the first period duration corresponds to a drive frequency in the range of 20 Hz to 250 Hz and the second period duration corresponds to a generator frequency in a range of 800 Hz to 3 kHz.

12. The circuit apparatus as claimed in claim 1 , wherein the AC voltage has a sinusoidal profile.

13. A switchable glazing assembly comprising:

at least one switchable glazing unit, and

the circuit apparatus as claimed in claim 1 .

14. A motor vehicle comprising the switchable glazing assembly as claimed in claim 13 .

15. A method for controlling a glazing unit whose transparency is switchable utilizing a circuit apparatus, wherein the circuit apparatus has a potential-isolated circuit part which, the method comprising:

to set a predefined transparency state on the glazing unit, at the circuit apparatus, generating a periodically alternating drive voltage which has a predetermined first period duration;

at a voltage source, to which the potential-isolated circuit part is connected via a transformer, operating the transformer with an AC voltage which has a second period duration shorter than the first period duration;

at the potential-isolated circuit part receiving a transformed AC voltage from the transformer and, in periodically alternating switching phases, respectively forwarding only positive half-cycles of the transformed AC voltage to an electrical capacitance of the glazing unit and forwarding only negative half-cycles of the transformed AC voltage to an electrical capacitance of the glazing unit utilizing a converter device controlled by a control device, wherein a duration of two successive switching phases corresponds to the first period duration.