Driving thin film switchable optical devices
Controllers and control methods apply a drive voltage to bus bars of a thin film optically switchable device. The applied drive voltage is provided at a level that drives a transition over the entire surface of the optically switchable device but does not damage or degrade the device. This applied voltage produces an effective voltage at all locations on the face of the device that is within a bracketed range. The upper bound of this range is associated with a voltage safely below the level at which the device may experience damage or degradation impacting its performance in the short term or the long term. At the lower boundary of this range is an effective voltage at which the transition between optical states of the device occurs relatively rapidly. The level of voltage applied between the bus bars is significantly greater than the maximum value of the effective voltage within the bracketed range.
1. A controller for controlling an optical state of an optically switchable device, the controller comprising:
circuitry for applying voltage or providing instructions to apply voltage between bus bars on the optically switchable device; and
a processing component configured to cause:
applying a ramp function to the voltage applied to the bus bars to drive the optically switchable device until one or more regions of the optically switchable device achieves a predetermined voltage;
after the one or more regions of the optically switchable device achieves the predetermined voltage,
(a) reducing the voltage applied to the bus bars to generate a reduced magnitude voltage; and
(b) reducing a current delivered to the optically switchable device, wherein a profile of the current as a function of time is shaped in accordance with a profile of the reduced magnitude voltage applied to the optically switchable device.
2. The controller of claim 1 , wherein the reduced magnitude voltage comprises a value of about 1 V or less.
3. The controller of claim 1 , wherein the controller is attached to or integrated in an insulated glass unit that comprises the optically switchable device.
4. The controller of claim 1 , wherein the controller is configured to provide an alarm before the voltage applied to the bus bars reaches a maximum safe voltage.
5. The controller of claim 4 , wherein the maximum safe voltage is between about 5-9 V.
6. The controller of claim 1 , wherein after the one or more regions of the optically switchable device achieves the predetermined voltage and prior to (a), the predetermined voltage is maintained until a specified condition is met.
7. The controller of claim 6 , wherein the specified condition is passage of a predetermined amount of time.
8. The controller of claim 6 , wherein the specified condition is delivery of a predetermined amount of charge to the optically switchable device.
9. A controller for controlling an optical state of an optically switchable device, the controller comprising:
circuitry for applying voltage or providing instructions to apply voltage between bus bars on the optically switchable device; and
a processing component configured to cause:
applying a ramp function to a voltage to drive the optically switchable device until one or more regions of the optically switchable device achieves a predetermined voltage; and
after the one or more regions of the optically switchable device achieves the predetermined voltage, reducing a magnitude of the voltage to generate a reduced magnitude voltage, such that a current delivered to the optically switchable device has a profile that is shaped in accordance with a profile of the reduced magnitude voltage, in which the profile is shaped as a function of time.
10. The controller of claim 9 , wherein the reduced magnitude voltage comprises a value of at most about 1 V.
11. The controller of claim 9 , wherein the controller is attached to or integrated in an insulated glass unit that comprises the optically switchable device.
12. The controller of claim 1 , wherein the controller is configured to provide an alarm before the voltage applied to the bus bars reaches a maximum safe voltage.
13. The controller of claim 12 , wherein the maximum safe voltage is between about 5-9 V.
14. The controller of claim 1 , wherein after the one or more regions of the optically switchable device achieves the predetermined voltage and prior reducing the magnitude of the voltage to generate the reduced magnitude voltage, the predetermined voltage is maintained until a specified condition is met.
15. The controller of claim 14 , wherein the specified condition is passage of a predetermined amount of time.
16. The controller of claim 14 , wherein the specified condition is delivery of a predetermined amount of charge to the optically switchable device.
17. A controller for controlling an optical state of an optically switchable device, the controller comprising:
circuitry for applying voltage or providing instructions to apply voltage between bus bars on the optically switchable device; and
a processing component configured to cause:
during a first phase, controlling current conducted to the optically switchable device;
terminating the first phase responsive to one or more regions of the optically switchable device attaining a predetermined voltage magnitude; and
after the first phase, controlling a voltage applied to the optically switchable device, wherein a profile of a current conducted to the optically switchable device is in accordance to a profile of the applied voltage.
18. The controller of claim 17 , wherein the current conducted during the first phase conducts from a first conductive layer to a second conductive layer of the optically switchable device, the conducted current causing movement of ions in the optically switchable device to bring about an electrochromic phenomenon.
19. The controller of claim 18 , wherein the current conducted in the first phase causes movement of one or more lithium ions within the optically switchable device.
20. The controller of claim 18 , wherein the controller is attached to or integrated in an insulated glass unit that comprises the optically switchable device, wherein the first and the second conductive layers each comprise a material selected from the group consisting of indium oxide, indium tin oxide, doped indium oxide, tin oxide, doped tin oxide, zinc oxide, aluminum zinc oxide, doped zinc oxide, ruthenium oxide, and doped ruthenium oxide.