U.S. patent application number 10/442719 was filed with the patent office on 2003-11-13 for method and apparatus for controlling an electrochromic device.
Invention is credited to Backfisch, David L., Coleman, Charles R., Yu, Phillip C..
Application Number | 20030210450 10/442719 |
Document ID | / |
Family ID | 24584535 |
Filed Date | 2003-11-13 |
United States Patent
Application |
20030210450 |
Kind Code |
A1 |
Yu, Phillip C. ; et
al. |
November 13, 2003 |
Method and apparatus for controlling an electrochromic device
Abstract
A method and apparatus for controlling a charge/discharge
voltage applied to an EC device to ensure that an appropriate
voltage drop across the EC device is maintained during charge
and/or discharge modes of operation. The appropriate voltage drop
is determined with respect to a temperature measurement proximate
the EC device. The charge level of the device is monitored using a
coulomb counter circuit having a topology designed to minimize
interference in the operation of the EC device.
Inventors: |
Yu, Phillip C.;
(Murrysville, PA) ; Backfisch, David L.;
(Monroeville, PA) ; Coleman, Charles R.;
(Pittsburgh, PA) |
Correspondence
Address: |
PPG INDUSTRIES INC
INTELLECTUAL PROPERTY DEPT
ONE PPG PLACE
PITTSBURGH
PA
15272
US
|
Family ID: |
24584535 |
Appl. No.: |
10/442719 |
Filed: |
May 21, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10442719 |
May 21, 2003 |
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09644355 |
Aug 23, 2000 |
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6614577 |
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Current U.S.
Class: |
359/265 ; 351/44;
359/275; 359/288 |
Current CPC
Class: |
G02F 1/163 20130101 |
Class at
Publication: |
359/265 ;
359/275; 359/288; 351/44 |
International
Class: |
G02F 001/15; G02F
001/153; G02F 001/01; G02C 007/10 |
Claims
1. Apparatus for controlling a charge state of an electrochromic
(EC) device, comprising: a controllable voltage source, for
providing a charging voltage to said EC device; a temperature
sensor, for providing an indicium of a temperature proximate said
EC device; and a controller, for determining, in response to said
temperature indicium, an appropriate voltage to be applied to said
EC device by said controllable voltage source, said determined
voltage defining a rate of charge.
2. The apparatus of claim 1, further comprising: a charge counter,
for counting charge quanta imparted to said EC device; said
controller causing said controllable voltage source to stop
producing said changing voltage when said charge quanta imparted to
said EC device reaches a desired level.
3. The apparatus of claim 2, further comprising: a polarity
reversal circuit, for selectively applying said voltage produced by
said controllable voltage source to said EC device as one of a
charge current and a discharge voltage.
4. The apparatus of claim 2, wherein said charge counter comprises:
a current mirror, for producing a reference current proportional to
said current produced by said controllable voltage source; and a
switch, selectively coupling said reference current to a capacitor,
for repeatedly causing said capacitor to be charged to a first
threshold level and discharged to a second threshold level by said
reference current; wherein a pulse is provided to said controller
each time said capacitor is charged to said first threshold level
and each time said capacitor is discharged to said second threshold
level.
5. The apparatus of claim.4, further comprising: a counter, said
counter being incremented in response to pulses provided during a
charge mode and decremented in response to pulses provided during a
discharge mode, said count being indicative of a present charge
level of said EC device.
6. The apparatus of claim 5, wherein said charge level of said EC
device Q.sub.EC is approximately defined by the following equation:
C.sub.REF*2(V.sub.H-V.sub.L)*COUNT where: C.sub.REF is the
capacitance of the reference capacitor; COUNT is the presently
stored counter value; V.sub.H is the first threshold level; and
V.sub.L is the second threshold level.
7. The apparatus of claim 1, wherein: said controllable voltage
source provides a charging voltage across said EC device; and said
appropriate voltage to be produced by said controllable voltage
source comprises a charging voltage bounded by a minimum charge
voltage and a maximum charge voltage, said minimum and maximum
charging voltages being temperature dependent.
8. The apparatus of claim 7, wherein said maximum charge level is
selected to avoid browning or bubbling of said EC device.
9. The apparatus of claim 7, wherein said minimum charge level is
selected to provide a minimum rate of chromatic change within said
EC device.
10. Apparatus for controlling a charge state of an electrochromic
(EC) device, said electrochromic device receiving a charging
current said apparatus comprising: a reference impedance, coupled
to receive a reference current proportional to said charging
current, said reference impedance having a known impedance
relationship with said electrochromic device; a window comparator,
coupled to said reference impedance, for comparing a voltage level
of said reference impedance to upper and lower threshold levels and
producing an output signal indicative of said comparison; and a
controller, coupled to said window comparator, for determining a
charge level of said EC device using said window comparator output
signal.
11. The apparatus of claim 10, further comprising: a temperature
sensor, for determining a temperature proximate said electrochromic
device; said controller, in response to said determined
temperature, determining an appropriate charging voltage for said
EC device and adapting said charging voltage to said appropriate
charging voltage.
12. The apparatus of claim 8, wherein said appropriate charge
voltage is bounded by a minimum charge voltage and a maximum charge
voltage, said minimum and maximum charging voltages being
temperature dependent.
13. In eyewear having a lens portion optically cooperating with an
electrochromic material, apparatus for controlling a charge state
of said electrochromic material, comprising: a controllable current
source, for providing a current to said electrochromic device; a
charge counter, for counting charge quanta imparted to said
electrochromic device; a temperature sensor, for providing an
indicium of a temperature proximate said electrochromic device; and
a controller, for determining, in response to said temperature
indicium,, an appropriate voltage to be produced by said
controllable current source; said controller causing said current
source to stop producing said current when said charge quanta
imparted to said electrochromic device reaches a desired level.
14. The apparatus of claim 13, further comprising: a polarity
reversal circuit, for selectively applying said current produced by
said controllable current source to said electrochromic device as
one of a charge current and a discharge current.
15. The apparatus of claim 13, wherein said charge counter
comprises: a current mirror, for producing a reference current
proportional to said current produced by said controllable current
source; and a switch, selectively coupling said reference current
to a capacitor, for repeatedly causing said capacitor to be charged
to a first threshold level and discharged to a second threshold
level by said reference current; wherein a pulse is provided to
said controller each time said capacitor is charged to said first
threshold level and each time said capacitor is discharged to said
second threshold level.
16. The apparatus of claim 15, further comprising: a counter, said
counter being incremented in response to pulses provided during a
charge mode and decremented in response to pulses provided during a
discharge mode, said count being indicative of a present charge
level of said electrochromic device.
17. The apparatus of claim 15, wherein said charge level of said
electrochromic device Q.sub.EC is approximately defined by the
following equation: C.sub.REF*2(V.sub.H-V.sub.L)*COUNT where:
C.sub.REF is the capacitance of the reference capacitor; COUNT is
the presently stored counter value; V.sub.H is the first threshold
level; and V.sub.L is the second threshold level.
18. The apparatus of claim 13, wherein: said controllable current
source induces a charging voltage across said electrochromic
device; and said appropriate current~to be produced by said
controllable current source comprises a current that produces a
charging voltage bounded by a minimum charging voltage and a
maximum charging voltage, said minimum and maximum charging
voltages being temperature dependent.
19. Apparatus for controlling a charge state of an electrochromic
device, comprising: a controllable voltage source, for providing a
charging voltage to said electrochromic device; a charge counter,
for counting charge quanta imparted to said electrochromic device;
a temperature sensor, for providing an indicium of a temperature
proximate said electrochromic device; and a controller, for
determining, in response to said temperature indicium, an
appropriate voltage to be applied to EC device by said controllable
current source; said controller causing said current source to stop
producing said current when said charge quanta imparted to said
electrochromic device reaches a desired level.
20. The apparatus of claim 19, further comprising: a polarity
reversal circuit, for selectively applying said voltage produced by
said controllable voltage source to said electrochromic device as
one of a charge current and a discharge current.
21. The apparatus of claim 19, wherein said charge counter
comprises: a current mirror, for producing a reference current
proportional to said current produced by said controllable current
source; and a switch, selectively coupling said reference current
to a capacitor, for repeatedly causing said capacitor to be charged
to a first threshold level and discharged to a second threshold
level by said reference current; wherein a pulse is provided to
said controller each time said capacitor is charged to said first
threshold level and each time said capacitor is discharged to said
second threshold level.
22. The apparatus of claim 21, further comprising: a counter, said
counter being incremented in response to pulses provided during a
charge mode and decremented in response to pulses provided during a
discharge mode, said count being indicative of a present charge
level of said electrochromic device.
23. The apparatus of claim 22, wherein said charge level of said
electrochromic device Q.sub.EC is approximately defined by the
following equation: C.sub.REF*2(V.sub.H-V.sub.L)*COUNT where:
C.sub.REF is the capacitance of the reference capacitor; COUNT is
the presently stored counter value; V.sub.H is the first threshold
level; and V.sub.L is the second threshold level.
24. A method for maintaining charge delivered to an electrochromic
device at a predetermined level as the temperature proximate said
device varies, wherein said charge is induced by an applied
voltage, said method comprising the steps of: (a) sensing the
temperature proximate said device; and (b) adjusting said applied
voltage in accordance with the temperature sensed in step (a) so as
to maintain said charge at said predetermined level.
25. The method of claim 24, wherein said device is an
electrochromic lens.
26. The method of claim 24, wherein the polarity of said applied
voltage is adapted to selectively increase and decrease said
charge.
27. The method of claim 24, wherein said applied voltage is bounded
by a minimum charging voltage and a maximum charging voltage, said
minimum and maximum charging voltages being temperature
dependent.
28. A method for maintaining charge delivered to an electrochromic
device at a predetermined level as the temperature proximate said
device varies, wherein said charge is induced by an applied
current, said method comprising the steps of: (a) sensing the
temperature proximate said device; and (b) adjusting said applied
current in accordance with the temperature sensed in step (a) so as
to maintain said charge at said predetermined level.
29. The method of claim 28, wherein said device is an
electrochromic lens.
30. The method of claim 28, wherein the polarity of said applied
current is adapted to selectively increase and decrease said
charge.
31. The method of claim 28, wherein said applied current is bounded
by a minimum charging voltage and a maximum charging voltage, said
minimum and maximum charging voltages being temperature
dependent.
32. A method for adapting the charge level of an electro-optic
device, comprising the steps of: (a) sensing the temperature
proximate said device; and (b) simultaneously adjusting a rate of
charge and a maximum charging voltage in accordance with the sensed
temperature to achieve a desired charge level in said electro-optic
device.
33. The method of claim 32, wherein said electro-optic device
comprises an electrochromic device.
34. The method of claim 32, wherein said electro-optic device
optically cooperates with one of a lens, a vehicle windshield and a
window pane.
35. The method of claim 32, wherein said method is performed by a
controller within an eyewear housing, said eyewear housing
including a lens that optically cooperates with said electro-optic
device and a power source for providing said charging voltage.
36. The method of claim 35, wherein said power source comprises one
of a battery, a fuel cell and a solar cell.
37. A method, comprising the step of: simultaneously controlling,
according to a temperature proximate an electrochromic (EC) device,
a total charge applied to the EC device and a rate at which the
charge is applied to the EC device.
38. The method of claim 37, further comprising the step of:
adapting said applied charge to a determination that a desired
charge level has been reached.
Description
[0001] The invention relates to the control of electrochromic
devices, more particularly, the invention relates to a method and
apparatus suitable for use in controlling a charge level of an
electrochromic device.
BACKGROUND OF THE DISCLOSURE
[0002] The optical properties of electrochromic materials change in
response to electrically driven changes in oxidation state. Thus,
when an applied voltage from an external power supply causes
reduction or oxidation of an electrochromic material, its
transmittance properties change. In order to maintain charge
neutrality, a charge balancing flow of ions in the electrochromic
device is needed. By enabling the required electron and ion flows
to occur, an electrochromic device utilizes reversible oxidation
and reduction reactions to achieve optical switching.
[0003] Conventional electrochromic devices comprise at least one
thin film of a persistent electrochromic material, i.e., a material
which, in response to application of an electric field of given
polarity, changes from a high-transmittance, non-absorbing state to
a low-transmittance, absorbing or reflecting state. Since the
degree of optical modulation is directly proportional to the charge
transfer induced by the applied voltage, electrochromic devices
demonstrate light transmission tunability between
high-transmittance and low-transmittance states. In addition, these
devices exhibit long-term retention of a chosen optical state,
requiring no power consumption to maintain that optical state.
Optical switching occurs when an electric field of reversed
polarity is applied.
[0004] To facilitate the aforementioned ion and electron flows, an
electrochromic film which is both an ionic and electronic conductor
is in direct physical contact with an ion-conducting material
layer. The ion-conducting material may be inorganic or organic,
solid, liquid or gel, and is preferably an organic polymer. The
electrochromic film(s) and ion-conductive material are disposed
between two electrodes, forming a laminated cell.
[0005] When the transparent conductive electrode, adjacent to the
electrochromic film, is the cathode, application of an electric
current causes darkening of the film. Reversing the polarity causes
electrochromic switching, and the film reverts to its
high-transmittance state. Typically, an electrochromic film such as
tungsten oxide is deposited on a substrate coated with a
transparent conductive film such as tin oxide or indium tin oxide
to form one electrode.
[0006] Since an electrochromic device may be modeled as a
non-linear passive device having an impedance dominated by a
capacitive component, the amount of charge transferred to an
electrochromic device is typically controlled by potential sources
or current sources and current sinks.
[0007] In a known arrangement for controlling an EC device, an
up/down counter is responsive to an up/down signal and a clock
signal to produce a digital word representative of a desired EC
charge level. Control logic is used to convert the digital word to
a current source/sink programming signal suitable for causing a
current source (or sink) to impart the desired charge level to the
EC device.
[0008] Unfortunately, the above arrangement utilizes various
components (e.g., current source and current sink transistors)
having characteristics that tend to drift over time and
temperature, thereby imparting more or less charge to the EC device
than is otherwise indicated by the digital word produced by the
up/down counter. In addition, EC devices themselves are subject to
operational degradation over time and temperature. Moreover, the
amount of energy required to charge an EC device is typically
greater than the amount of energy required to discharge such a
device. Thus, over a given period of time or temperature, an EC
charge error may be accumulated such that the EC device may be
significantly lighter or darker than desired.
[0009] A paper by J. P. Matthews et al., "Effect of Temperature on
Electrochromic Device Switching Voltages," Electrochimica Acta 44
(1999), discloses that switching voltages needed to color
electrochromic devices vary with temperature. However, the paper
does not disclose or suggest a method or apparatus for maintaining
the charge delivered to an electrochromic device at a predetermined
level.
SUMMARY OF THE INVENTION
[0010] The instant invention is directed to a method for delivering
a substantially constant, predetermined charge to an
Velectrochromic device, said method having a voltage compensation
or adjustment requirement feature relative to varying ambient
temperatures, and to an apparatus for use in an electrochromic (EC)
control system in which components causing the charging and
discharging of an electrochromic device are subject to drift errors
and other errors.
[0011] The invention controls a charge/discharge voltage (or
current) profile applied to an EC device to ensure that an
appropriate voltage drop across the EC device is limited and/or
maintained during charge and/or discharge modes of operation. The
appropriate voltage drop is determined with respect to a
temperature measurement proximate (i.e., near, on or within) the EC
device. since the charge/discharge rate is defined by the voltage
drop, a factor in the selection of an appropriate voltage is the
appropriate charge/discharge rate of the device being controlled.
The charge level of the device is monitored using a coulomb counter
circuit having a topology designed to minimize interference in the
operation of the EC device.
[0012] The invention simultaneously controls the total charge
applied to an EC device and the rate at which that charge is
applied to the EC device over a functional temperature range to
control the EC device within a stable electrochemical limit to
provide a useful lifecycle durability. A maximum rate of charge
transfer is selected to avoid secondary electrochemical reactions
of the controlled EC device. In one embodiment, a minimum rate of
charge transfer may be provided to ensure that a minimum desirable
rate of operation of the controlled EC device is maintained.
[0013] Specifically, the instant invention is directed to a method
for controlling the rate of charge delivered to, or removed from,
an electrochromic device, while maintaining the charge delivered
to, or removed from, the electrochromic device at a predetermined
or programmed level, where each of a plurality of levels
corresponds to respective bleached or colored states, as the
temperature proximate (i.e., near, on or within) the device varies,
the method comprising the steps of: (a) sensing the temperature
proximate the device; and (b) adjusting the voltage or current
applied to the device based on the temperature sensed in step
(a).
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The teachings of the present invention can be readily
understood by considering the following detailed description in
conjunction with the accompanying drawings, in which:
[0015] FIG. 1 depicts a block diagram of an electrochromic control
apparatus;
[0016] FIG. 2 depicts an embodiment of a controller suitable for
use in the electrochromic control apparatus of FIG. 1;
[0017] FIG. 3 depicts a circuit of a charge counter suitable for
use in the electrochromic control apparatus of FIG. 1; and
[0018] FIG. 4 depicts a flow diagram of a control method suitable
for use in the electrochromic control apparatus of FIG. 1 and the
controller of FIG. 2.
[0019] To facilitate understanding, identical reference numerals
have been used, where possible; to designate identical elements
that are common to the figures.
DETAILED DESCRIPTION
[0020] The invention will be described within the context of
controlling the charge level of an electrochromic device. However,
it will be appreciated by those skilled in the art that since
electrochromic devices form a subset of the broader category of
electro-optic devices, the invention is equally applicable to other
electro-optic devices, especially those that benefiting from a
well-controlled charge and/or discharge methodology and apparatus,
such as described below. Moreover, portions of the description
referring to the charge transferred to a device intended to reflect
that charge is transferred between electrodes that are located, for
example, within the device. For purposes of this discussion, a
device is primarily defined as an electro-optic (e.g.,
electrochromic) cell or cells having respective associated
conductors used to transfer charge. The invention advantageously
provides for the operation of an EO or EC device over a long period
of time without a side reaction that visibly degrades the
performance of the device.
[0021] FIG. 1 depicts an electrochromic control apparatus 100
including charge error correction apparatus according to the
invention. The electrochromic control apparatus 100 is used to
control the amount of charge imparted to an electrochromic device
EC. Since the electrochromic device EC may be modeled as a
non-linear passive device having an impedance dominated by a
capacitive component, the electrochromic device EC is depicted in
FIG. 1 as a capacitor having a first terminal (denoted as 1) and
second terminal (denoted as 2).
[0022] In response to a coloring current I.sub.COLOR applied to the
electrochromic device EC at the first terminal 1, the charge of the
electrochromic device EC increases, thereby causing the device to
darken. In response to a bleaching current I.sub.BLEACH, the charge
of the electrochromic device EC decreases, thereby causing the
electrochromic device EC to lighten. One skilled in the art will
readily recognize that the polarities of the coloring current
I.sub.COLOR and the bleaching current I.sub.BLEACH may be reversed,
depending on the connection and type of electrochromic device EC
employed.
[0023] The electrochromic control apparatus 100 comprises a voltage
reference 105, a battery 108, a user interface 110, a controller
200, a digital to analog (D/A) converter 115, a power converter
120, an analog to digital (A/D) converter 140, a temperature sensor
145, a charge counter 300, a polarity reversal circuit 125, a
sensing resistor R1 and the electrochromic device EC to be
controlled.
[0024] The battery 108 is used to provide all power within the
apparatus 100. The battery has a positive terminal denoted as +V
and a negative terminal denoted as ground. The voltage reference
105 is powered by the battery 108 and includes an output terminal
for providing a controlled voltage reference signal VREF. The
voltage reference signal VREF is coupled to the D/A converter 115,
A/D converter 140 and charge counter 300.
[0025] The user interface 110 may comprise a series of push buttons
or other user interface means suitable for providing information to
controller 200 indicative of a desire to lighten (bleach) B or
darken (color) C the electrochromic device EC. In response to the
user interface signals B and C provided by the user interface 110,
the controller 200 causes the electrochromic device EC to be
lightened or darkened respectively.
[0026] The controller 200 provides a first output signal VCONT
indicative of the maximum voltage limit to be applied to the
electrochromic device EC. This voltage limit which is determined by
the controller 200 is a function of temperature. The first output
signal VCONT of the controller is converted to an analog power
control signal PC by the D/A converter 115 and coupled to the power
converter 120.
[0027] Power converter comprises a controllable voltage source 120.
In response to an increase or decrease in the voltage level of
power control signal PC, the power converter 120 respectively
increases or decreases its output voltage. The input current drawn
from the battery for use in the power conversion is limited by the
power converter in order to prolong battery life. The output
current I and output voltage V provided by the power converter 120
is coupled to the polarity reversal circuit 125 for subsequent
application to the electrochromic device EC to effect a charging
(darkening or coloring) or discharging (lightening or bleaching) of
the electrochromic device EC. It should be noted that while power
converter 120 is described as a controllable voltage source, in an
alternate embodiment of the invention power converter 120 comprises
a controllable current source. In either case, power converter 120
is controllably operated to adapt the charge or discharge level of
the electrochromic device EC to an appropriate charge or discharge
level.
[0028] The controller 200 provides a second output signal CHARGE
indicative of a desired "charge" mode of operation, and a third
output signal DISCHARGE indicative of a desired "discharge" mode of
operation.. The second CHARGE and third DISCHARGE control signals
are coupled to the polarity reversal circuit 125.
[0029] The polarity reversal circuit comprises, illustratively,
four switches SWA-SWD arranged in a bridge configuration to
selectively couple the current I produced by the power converter
120 to the EC device in either the charge mode or the discharge
mode of operation.
[0030] Each of switches SWA-SWD comprises a 1FormA (single pole
single throw) switch having a respective input terminal, output
terminal and control terminal. The output current I from power
converter 120 is coupled to the input terminals of switches SWA and
SWC. The output terminal of switch SWA is connected to the input
terminal of switch SWB. The output terminal of switch SWC is
connected to the input terminal of switch SWD. The output terminals
of switches SWB and SWD are coupled to ground. The electrochromic
device EC is coupled in series between the output terminals of
switches SWA and SWC, in the known bridge configuration.
[0031] In the charge mode of operation, the control signal CHARGE
is used to cause switches SWA and SWD to close, while the control
signal DISCHARGE is used to cause switches SWB and SWC to open. In
this mode of operation, the current flows from power converter 120
through, resistor R1, switch SWA, the electrochromic device EC and
switch SWD to ground. During the charge mode of operation, current
flowing through the electrochromic device EC imparts charge to the
electrochromic device, thereby causing the device to darken or
color.
[0032] In the discharge mode of operation, the control signal
CHARGE is used to cause switches SWA and SWD to open, while the
control signal DISCHARGE is used to cause switches SWB and SWC to
close. In this mode of operation, the current flows from power
converter 120 through resistor R1, switch SWC, the electrochromic
device EC, and switch SWB to ground- During the discharge mode of
operation, current flowing through the electrochromic device EC
removes charge from the electrochromic device, thereby causing the
device to lighten or bleach.
[0033] As previously noted, the electrochromic device EC may be
characterized as a nonlinear device having both capacitive and
resistive components. Therefore, the amount of charge imparted to
the EC device is roughly defined by the equation: Q=CV, where Q is
equal to the charge as measured in Coulombs, C is equal to
capacitance of the EC device as measured in Farads, and V is equal
to charging voltage as measured in Volts.
[0034] It is critical to note that an appropriate charging (or
discharging) voltage for an electrochromic device is temperature
dependent. Moreover, the appropriate charge and discharge voltage
differs between various electro-optic and electrochromic devices,
depending upon the EO or EC device construction. The appropriate
charge and discharge voltage is bounded by minimum and maximum
voltage levels, both of which are temperature dependent.
[0035] The appropriate voltage drop is determined with respect to a
temperature measurement proximate (i.e., near, on or within) the EC
device. since the charge/discharge rate is defined by the voltage
drop, a factor in the selection of an appropriate voltage is the
appropriate charge/discharge rate of the device being controlled.
The charge level of the device is monitored using a coulomb counter
circuit having a topology designed to minimize interference in the
operation of the EC device. The inventors have recognized that the
maximum voltage drop across the electrochromic device varies with
temperature and that voltage drops beyond the allowed maximum will
result in damage to the electrochromic device. It is further
recognized that voltage drops below the voltage minimum at the
specified temperature will degrade the desired product performance
by increasing the charge and discharge time but will not damage the
EC device. Advantageously, the subject invention controls the
electrochromic device EC in a manner that adapts to temperature
changes.
1TABLE 1 VOLTAGE MAX VOLTAGE MIN TEMP (F.) TEMP (C.) (COLOR)
(COLOR) 66.2 19 1.267 1.237 68 20 1.255 1.225 69.8 21 1.244 1.214
71.6 22 1.233 1.203 73.4 23 1.222 1.193 75.2 24 1.212 1.183 77 25
1.203 1.174 78.8 26 1.193 1.166 80.6 27 1.185 1.158 82.4 28 1.177
1.150 84.2 29 1.169 1.143 86 30 1.161 1.136
[0036] Table 1 depicts a tabular representation of maximum and
minimum coloring (charging) voltages for an exemplary
electrochromic device based on temperature. Similarly, Table 2
depicts a tabular representation of maximum and minimum bleaching
(discharging) voltages across exemplary electrochromic device
depending on temperature. The negative polarity indication of the
Table 2 voltages reflects the relative polarity of the discharge
voltage applied to the EC device during the discharge mode of
operation.
[0037] Referring to Table 1 and assuming an ambient temperature of
77 F. (25 C.), the maximum coloring voltage is 1.203 Volts, while
the minimum coloring voltage is 1.174 Volts. That is, the current I
passed through the electrochromic device during the charge mode of
operation must produce a voltage drop having a minimum voltage of
1.174 Volts and a maximum voltage of 1.203 Volts. The controller
200 operates to ensure that these limits are adhered to. Similarly,
at the same temperature a colored (i.e., charged) electrochromic
device must be bleached at a minimum voltage of 0.529 Volts and a
maximum voltage of 0.599 Volts
2TABLE 2 VOLTAGE MAX VOLTAGE MIN TEMP (F.) TEMP (C.) (BLEACH)
(BLEACH) 66.2 19 -0.730 -0.650 68 20 -0.706 -0.627 69.8 21 -0.683
-0.605 71.6 22 -0.660 -0.584 73.4 23 -0.639 -0.565 75.2 24 -0.618
-0.546 77 25 -0.599 -0.529 78.8 26 -0.580 -0.513 80.6 27 -0.563
-0.498 82.4 28 -0.546 -0.484 84.2 29 -0.530 -0.472 86 30 -0.515
-0.461
[0038] Charge counter 300 senses the voltage VR1 across resistor
R1, converts that voltage measurement into a quantized current
measurement and provides indicia of that quantized current
measurement to controller 200 as a counter signal via a count
signal path. In this manner, controller 200 may determine the
actual charge level of the electrochromic device EC. Therefore, the
voltage across resistor R1 (VR1) is proportional to the charge or
discharge current. The charge counter 300 uses this voltage to
produce a current (I2, I3) proportional to the charge or discharge
current I. That is, 1 I 2 I R 1 R 2 .
[0039] The resulting current is used to repetitively charge and
discharge a capacitor C2 having a known capacitance, such that each
charge/discharge cycle of the known capacitor represents the
imparting (or removing from) a predetermined quanta of charge from
the EC device.
[0040] The charge counter 300 produces a pulse on an output signal
path coupled to the controller 200 each time the charge level of
the capacitor C2 exceeds an upper threshold level and each time the
charge level of the capacitor C2 passes below a lower threshold
level. The controller 200 responsively counts the number of pulses
and stores the result in a counter storage location in a memory. In
the case of the controller 200 causing the system to operate in the
charge mode, received pulses are used to increment the counter
location; in the case of the controller 200 causing the system to
operate in the discharge mode, received pulses are used to
decrement the counter location. Each pulse represents a quanta of
charge (.DELTA.q), the number of quanta of charge (n) multiplied by
the quanta of charge (.DELTA.q) equals the total charge, i.e.
Q=n.times.n..DELTA.q. The total charge represented by the counter
is further scaled by the values of resistors R1, R2 and capacitor
C2 and the gain of the sample and hold circuit.
[0041] Temperature sensor 145 detects ambient temperature or,
alternatively, the actual temperature of the electrochromic device
EC. In the exemplary embodiment of FIG. 1, temperature sensor 145
provides an indicium, such as an analog indication, of that
temperature to A/D converter 140. A/D converter 140 responsively
converts that analog temperature signal T to a digital temperature
word or signal TD that is coupled to the controller 200 for further
processing. It is noted that the temperature sensor 145 may be
located near, on or within the EC device. The above-described
embodiment of the invention contemplates the use of a power
converter 120 comprising a controllable voltage source. That is,
the control signal PC controls the output voltage of the power
converter 120 such that the voltage drop across the electrochromic
device EC causes a current to pass through the electrochromic
device proportional to the impedance of the electrochromic device.
As previously noted, it is also contemplated that power converter
120 may be a controllable current source. That is, the control
signal PC controls the output current of the power converter 120
such that the current flowing to the EC device is determined with
respect to the control signal PC. In a preferred embodiment of the
invention utilizing a battery, the power converter 120 comprises a
controllable voltage source. Within the context of battery powered
operation, a controllable voltage source is desirable because the
output voltage of the power converter 120 may be reduced as
necessary to insure that the current drawn from the battery does
not exceed a predefined upper limit. In this manner, a topology
utilizing a controllable voltage source power converter 120
advantageously adapts the teachings of the present invention to the
realities of batteries having finite current sourcing capabilities.
FIG. 3 depicts a schematic diagram of a charge counter circuit
suitable for use in the electrochromic control system of FIG. 1.
Specifically, the charge counter circuit 300 comprises a sample and
hold circuit 310, a buffer 320, a current mirror circuit 330 and a
comparator circuit 340. Charge counter 300 senses the voltage VR1
across resistor R1, converts that voltage measurement into a
quantized current measurement and provides indicia of that
quantized current measurement to controller 200 as a counter signal
via a count signal path. By determining this charge, the controller
200 of the present invention may more accurately provide
appropriate bleaching and/or darkening of the electrochromic
device.
[0042] The sample and hold circuit 310 operates to sample the
voltage across resistor R1 and hold the sampled voltage on a
capacitor with one side referenced to ground point. It should be
noted that resistor R1 is floating with respect to ground. Sample
and hold circuit 310 comprises a sample and hold module SH and a
capacitor C1. The sample and hold module SH receive the positive
sense line SENSE+ and negative sense line SENSE- from the resister
R1. The sample and hold module periodically samples the voltage
across resister R1 provided via the sense lines SENSE+ and SENSE-
to produce a sampled voltage V(I). The capacitor C1 is coupled
between the output of sample and hold module SH and ground.
Capacitor C1 operates to store, or hold, the sampled voltage V(I)
produced by sample and hold module SH. The sampled voltage V(I) is
proportional to the sampled current through electrochromic device
EC.
[0043] Buffer 320 comprises a unity gain buffer that buffers the
output of sample and hold circuit 310 and produces a current I2
proportional to the sampled voltage V(I). Specifically, buffer 320
comprises an operational amplifier A1, a transistor Q1 and a
resistor R2. Operational amplifier A1 receives the sampled voltage
V(I) at a positive input terminal. operational amplifier A1 has a
negative input terminal connected to an output terminal of
transistor Q1, and an output terminal connected to a control
terminal of transistor Q1. Resistor R2 is coupled between the
output terminal of transistor Q1 and ground. An input terminal of
transistor Q1 receives a current I2 from current mirror 330.
[0044] Unity gain buffer 320 operates to keep the voltage across
resistor R2 substantially the same as the voltage across resistor
R1 (i.e., V(I)). The voltage across R2 is proportional to the
voltage across R1, and is kept substantially the same where the
gain of the differential amplifier within the sample and hold
circuit is 1. In this manner, current I2 is proportional to the
current I passing through the electrochromic device EC of FIG.
1.
[0045] Current mirror 330 comprises five transistors (Q2-Q6), each
of which have an input terminal, an output terminal and a control
terminal. Transistor Q2, illustratively a PMOS transistor, has its
input terminal coupled to V+ and its control and output terminals
coupled together such that transistor Q2 forms a current source.
The current I2 produced by the voltage drop across transistor Q2 is
provided to buffer circuit 320. As previously noted, buffer circuit
320 controls I2 such that the voltage across resistor R2 is equal
to the voltage across resistor R1. Therefore, current I2
approximates the current through the electrochromic device EC of
FIG. 1.
[0046] The control terminal of transistor Q2 is also coupled to
respective control terminals of transistors Q3 and Q4, both of
which comprise PMOS transistors. Transistors Q3 and Q4 have input
terminals coupled to V+. An output terminal of transistor Q3 is
coupled to a first input of a 1FormC (single pole double throw)
switch SWP within comparator circuit 340.
[0047] The output terminal of transistor Q4 is coupled to the input
terminal of transistor Q6 and the control terminals of transistors
Q5 and Q6. The output terminals of transistor Q6 and Q5 are both
connected to ground. The input terminal of transistor Q5 is
connected to a second input terminal of the 1FormC switch SWP in
comparator circuit 340.
[0048] The current mirror circuit 330 produces, in addition to
current I2, a pair of additional currents denoted as I3A and I3B.
I3A is a current sourced from the output terminal of transistor Q3,
I3B is a current sunk by the input terminal of transistor Q5.
Current I3A flows to an output of switch SWP when the switch SWP is
in "zero" position, while current I3B flows from the output of
switch SWP when the switch SWP is in "one" position.
[0049] Comparator circuit 340 comprises the 1FormC switch SWP, the
capacitor C2, a window comparator WC1, and a pair of divider
resistors RD1 and RD2. As previously noted, the first input (input
0) of switch SWP is coupled to the output terminal transistor Q3,
while the second input (input 1) of switch SWP is connected to the
input terminal of transistor Q5. The output terminal of switch SWP
is coupled to an input terminal IN of the window comparator WC1.
The capacitor C2 is coupled between the output terminal of switch
SWP and ground.
[0050] A high reference input H of window comparator WC1 is coupled
to the voltage reference VREF. The resistors RD1 and RD2 are
coupled in series in the order named between the voltage VREF and
ground. A low reference input L of window comparator WC1 is coupled
to the junction of resistors RD1 and RD2, where a reference voltage
VD is formed by dividing the reference voltage VREF.
[0051] The window comparator WC1 compares the voltage at its input
terminal IN to the voltages at its high H and low L reference input
terminals. For purposes of this discussion it will be assumed that
VREF is equal to 1.5 Volts and VD is equal to 1.0 Volts.
[0052] As the current I of FIG. 1 begins to flow through the
electrochromic device EC and the resistor R1, the voltage across R1
increases proportionately. Thus, the voltage across capacitor C1 of
sample and hold circuit 310 begins to increase, resulting in an
increase in current I2 to the buffer circuit 320. This causes an
increase in current I3A which passes through switch SWP (selecting
terminal 0 at this time) and through capacitor C2, charging
capacitor C2. As the voltage across capacitor C2 increases through
the high reference voltage (e.g., 1.5 Volts), the control output C
of window comparator WC1 changes from 0 to 1, thereby causing
switch SWP to select terminal 1 rather than terminal 0 to be
coupled to the output of the output of the switch. This causes
capacitor C2 to be discharged through transistors Q5 and Q6 via
current I3B. As capacitor C2 is discharged the voltage across C2
decreases. When the voltage across capacitor C2 decreases to the
divider voltage VD provided to the low reference input of the
window comparator WC1, the control output of the window comparator
WC1 transitions from 1 to 0, causing switch SWP to couple the 0
input to the switch output. In this manner, currents I3A and I3B
repetitively charge and discharge capacitor C2.
[0053] Each time that capacitor C2 is charged to the voltage
reference level at the high input terminal (e.g., 1.5 Volts) a low
to high logic transition is sent to the controller 200 via the
signal path COUNT. Similarly, each time capacitor C2 is discharged
by current I3B to the voltage VD of the low reference input, high
to low logic transition is sent to the controller 200 via the
signal path COUNT. Thus, for every two logic transitions (one
pulse) sent to the controller 200, the controller 200 determined
that the charge of the EC device has increased (charge mode) or
decreased (discharge mode) by an amount of charge related to the
high and low reference voltages and the capacitance of C2.
[0054] Charge within a capacitor is defined by the formula Q=CV,
where Q is equal to charge as measured in Coulombs, C is equal to
capacitance as measured in farads and V is equal to voltage as
measured in Volts. Since charge counter 300 provided 1 pulse for
each change in voltage level of capacitor C2 from 1V to 1.5 V and
back to 1V, each pulse from the charge counter is equal to a charge
of (0.5 v)C+(0.5V)C=(1V)C. In the case of a 1 farad capacitor,
therefore, each pulse is equal to 1 Coulomb. In a more like
scenario of a much smaller capacitor, such as a 0.1 microFarad
capacitor each pulse is equal to 0.1 micro Coulomb.
[0055] Thus, the charge level of the electrochromic device
(Q.sub.EC) is approximately defined by the following equation:
C.sub.REF*2(v.sub.H-V.sub.L)*COUNT
[0056] where:
[0057] C.sub.REF is the capacitance of the reference capacitor
C2;
[0058] COUNT is the charge per packet;
[0059] V.sub.H is the upper threshold voltage of the window
comparator; and
[0060] V.sub.L is the lower threshold voltage of the window
comparator.
[0061] In an, alternate embodiment of the invention, the charge
level of the electrochromic device (Q.sub.EC) is approximately
defined by the following equation:
Q.sub.E C=C.sub.REF.times.(COUNT).times.(V.sub.H-V.sub.L)
[0062] In this embodiment of the invention, the above relationship
is true only if the absolute value of I.sub.3 is equal to the
absolute value of I.sub.EC, which is equal to the absolute value of
V.sub.r1 divided by R.sub.1. In this embodiment of the invention
R.sub.1 is not equal to R.sub.2 and, therefore, I.sub.EC is not
equal to I.sub.2 or I.sub.3. Thus,
Q.sub.EC=K.times.C.sub.REF.times.COUNT.times.(V.sub.H-V.sub.L),
where K is a constant of proportionality equal to R.sub.2 divided
by R.sub.1.times.A.sub.SH, where A.sub.SH is the voltage gain of
the differential input sample and hold circuit 310, which is equal
to 1 in the present embodiment of the invention, by varying the
differential input sample and hold voltage gain to a value other
than 1, the alternate calculation for Q.sub.EC
[0063] In the exemplary embodiment of FIG. 3 transistors Q1, Q5 and
Q6 comprise NMOS transistors, while transistors Q2-Q4 comprise PMOS
transistors. It would be appreciated by those skilled in the art
that other transistors may be used and that other circuit
topologies may be used to achieve similar functions. Additionally,
while the current I.sub.2 is proportional to the current I, it
should be noted that I.sub.2 is much less than I. Therefore, the
capacitor C.sub.2 may be much less than the capacitance of the
electrochromic device EC. In this manner, the amount of power
required to implement the present invention is reduced.
[0064] FIG. 2 depicts an embodiment of a controller suitable for
use in the electrochromic control apparatus of FIG. 1.
Specifically, the controller 200 of FIG. 2 comprises a
microprocessor 220 as well as memory 230 for storing an EC control
method 400, at least one look-up table 235 and a counter variable
237. The microprocessor 220 cooperates with conventional support
circuitry 240 such as power supplies, clock circuits, cache memory
and the like as well as circuits that assist in executing the
software methods. As such, it is contemplated that some of the
process steps discussed herein as software processes may be
implemented within hardware, e.g., as circuitry that cooperates
with the microprocessor 220 to perform various steps.
[0065] The EC controller 200 also comprises input/output circuitry
210 that forms an interface between the microprocessor 220 and the
user interface 110, D/A converter 115, A/D converter 140, charge
counter 300 and polarity reversal switches SWA-SWD of FIG. 1.
[0066] Although the EC control apparatus 200 is depicted as a
general purpose computer that is programmed to perform EC control
functions in accordance with the present invention, the invention
can be implemented in hardware as an application specific
integrated circuit (ASIC). As such, the process steps described
herein are intended to be broadly interpreted as being equivalently
performed by software, hardware, or a combination thereof.
[0067] The controller 200 of the present invention executes an EC
control method 400 that will now be described with respect to FIG.
4.
[0068] FIG. 4 depicts a flow diagram of a control method suitable
for use in the controller 200 of FIG. 1 and FIG. 2. Specifically,
FIG. 4 depicts a flow diagram of a method 400 for adapting a charge
level of a electrochromic device in response to user input and
further in response to temperature, determined appropriate charge
voltage and actual charge level of the electrochromic device. The
temperature may be provided by, for example, temperature sensor
145; the actual charge level may be provided by, for example,
calculations made using the indicia of EC device charge quanta
increase or decrease provided by charge counter 300; and
appropriate charge voltage may be determined with respect to the
temperature information and a look-up table relating the
temperature information to the EC device being controlled.
[0069] The method 400 of FIG. 4 is entered at step 405 where the
counter variable is initialized to zero, and the EC device is
assumed to have no charge. The method 400 then proceeds to step
410.
[0070] At step 410, user input indicative of a change in
electrochromic charge state is received. The method 400 then
proceeds to step 420.
[0071] At step 420, the controller 200 determines the ambient
temperature or electrochromic device temperature. The method 400
then proceeds to step 430.
[0072] At step 430 the minimum and maximum charge or discharge
voltage is determined based upon the temperature determined at step
420 and the contents of the look-up table 235. The method 400 then
proceeds to step 440.
[0073] At step 440, the controller 200 causes the power converter
120 to supply a current I based on the determined minimum and
maximum charge or discharge voltage level. The method 400 then
proceeds to step 450.
[0074] At step 450, the desired EC charge level is compared to the
present EC charge level. That is, at step 450 the desired charged
level as indicated by the user input received at step 410 is
compared to the present charge level of the electrochromic device
EC. The present charge level is determined with respect to the
count signal COUNT provided by the charge counter of 300. As
previously discussed, the charge counter 300 outputs a series of
pulses to the controller 200 where each pulse indicates a
predefined increase or decrease in charge level of the
electrochromic device. Thus, by maintaining a count of pulses
provided by charge counter 300 and by increasing that count in
response to pulses received during a charge mode while decreasing
that count in response to pulses received during a discharge mode,
the controller 200 is able to determine the present charge level of
the electrochromic device EC. The method 400 then proceeds to step
460.
[0075] At step 460, the controller 200 causes the polarity reversal
circuit to apply the appropriate charge or discharge current to the
electrochromic device EC. The method 400 then proceeds to step
470.
[0076] At step 470, a query is made as to whether a desired charge
level has been reached. That is, as step 470 the present charge
level as indicated by the charge counter 300 is compared to the
desired charged level to determine whether the electrochromic
device is at an appropriate charge level (i.e., an appropriate
bleached or color level). If the query at step 470 is answered
affirmatively, then the method 400 proceeds to step 480 where it is
exited. If the query at step 470 is answered negatively, then the
method 400 repeats steps 420-470.
[0077] The above-described invention is particularly well suited
for battery powered electrochromic device applications, such for
controlling the charge level of electrochromic coatings on lenses
in, e.g., a pair of eyewear or eyeglasses (i.e., sunglasses). The
invention also finds applicability in areas such as automotive,
architectural and aircraft glass and/or glazing, advertising
displays and the like.
[0078] In one embodiment, the electro-optic or electrochromic
device optically cooperates with a lens(es) (prescription or
other), a vehicle windshield. a window pane, an aircraft
transparency or other transparent or translucent material. In an
eyewear embodiment, an eyewear housing includes a controller for
executing control methods according to the invention as well as a
power source for providing a charging voltage or current. The power
source may comprise a battery, a fuel cell, a solar cell or any
other power source capable of providing the appropriate charging
voltage or current. Preferably, the power source is small enough to
fit inside the form factor defined by the eyewear or a helmet
including the eyewear. A wearable power source is also contemplated
by the inventors.
[0079] It should be noted that a maximum charge level is preferably
selected to avoid browning or bubbling of the EO or EC device,
while a minimum charge level is selected to provide a minimum rate
of chromatic change of the EO or EC device. Thus, the maximum
charge level is selected to avoid device damage, while the minimum
charge level is selected to meet a minimum consumer expectation
with respect to product performance including the controlled EC
device.
[0080] The above-described embodiments of the invention, and other
embodiments that will now be apparent tot hose skilled in the art,
controls the total charge applied to an EC device and the rate at
which that charge is applied to the EC device over a functional
temperature range to control the EC device within a stable
electrochemical limit and thereby provide a useful lifecycle
durability. A maximum rate of charge transfer is selected to avoid
secondary electrochemical reactions of the controlled EC device. In
one embodiment, a minimum rate of charge transfer may be provided
to ensure that a minimum desirable rate of operation of the
controlled EC device is maintained.
[0081] Although various embodiments which incorporate the teachings
of the present invention have been shown and described in detail
herein, those skilled in the art can readily devise many other
varied embodiments that still incorporate these teachings.
* * * * *