U.S. patent application number 14/224710 was filed with the patent office on 2015-10-01 for dimmer with photo sensor and high/low clamping.
This patent application is currently assigned to General Electric Company. The applicant listed for this patent is General Electric Company. Invention is credited to Jeffrey Glenn FELTY.
Application Number | 20150282275 14/224710 |
Document ID | / |
Family ID | 52574423 |
Filed Date | 2015-10-01 |
United States Patent
Application |
20150282275 |
Kind Code |
A1 |
FELTY; Jeffrey Glenn |
October 1, 2015 |
DIMMER WITH PHOTO SENSOR AND HIGH/LOW CLAMPING
Abstract
Provided is a circuit for controlling a level of brightness of a
light electrically coupled to a dimming circuit including control
leads configured to provide a dimming control voltage to the
dimmable driver, the dimming control voltage having a permissible
voltage range. The circuit includes a photo sensor for detecting an
ambient light level in the vicinity of the light and a clamp
controller for selectively reducing the dimming control voltage to
a clamped voltage range less than the permissible voltage range.
Also included is a feedback controller for adjusting the dimming
control voltage in response to a detected ambient light level, the
dimming control voltage being within the clamped voltage range.
Inventors: |
FELTY; Jeffrey Glenn;
(Elyria, OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
General Electric Company |
Niskayuna |
NY |
US |
|
|
Assignee: |
General Electric Company
Niskayuna
NY
|
Family ID: |
52574423 |
Appl. No.: |
14/224710 |
Filed: |
March 25, 2014 |
Current U.S.
Class: |
315/152 ;
315/149 |
Current CPC
Class: |
H05B 47/11 20200101;
Y02B 20/40 20130101; Y02B 20/46 20130101; H05B 45/10 20200101; H05B
41/38 20130101 |
International
Class: |
H05B 37/02 20060101
H05B037/02; H05B 33/08 20060101 H05B033/08; H05B 41/38 20060101
H05B041/38 |
Claims
1. A circuit for controlling a level of brightness of a light
electrically coupled to a dimming circuit including control leads
configured to provide a dimming control voltage to the dimmable
driver, the dimming control voltage having a permissible voltage
range, the circuit comprising: a photo sensor for detecting an
ambient light level in the vicinity of the light; a clamp
controller for selectively reducing the dimming control voltage to
a clamped voltage range less than the permissible voltage range;
and a feedback controller for adjusting the dimming control voltage
in response to a detected ambient light level, the dimming control
voltage being within the clamped voltage range.
2. The circuit of claim 1, wherein the ambient light level is
detected by a photo sensor; wherein the permissible range include a
minimum and a maximum output voltage; and wherein the level of
brightness of the light is responsive to the dimming control
voltage.
3. The circuit of claim 1, wherein the dimming control voltage
decreases as more ambient light is detected by the photo
sensor.
4. The circuit of claim 1, wherein the dimming control voltage is
the voltage measured across the pair of low voltage control
leads.
5. The circuit of claim 1, wherein the dimming control voltage is
the voltage measured across the pair of low voltage control
leads.
6. The circuit of claim 1, wherein the clamped voltage range has a
high voltage limit set lower than the maximum output voltage.
7. The circuit of claim 1, wherein the clamped voltage range has a
low voltage limit set higher than the minimum output voltage.
8. The circuit of claim 1, wherein the actual ambient light level
detected by the photo sensor is compared to a desired ambient light
level and the feedback controller adjusts the dimming control
voltage to adjust the level of brightness of the light to cause the
actual ambient light level to converge toward the desired ambient
light level.
9. The circuit of claim 8, wherein the desired ambient light level
is set using a reference voltage controller.
10. The circuit of claim 1, wherein the dimmable driver is a
ballast for a fluorescent light.
11. The circuit of claim 1, wherein the dimmable driver is an LED
driver for an LED or LED array.
12. The circuit of claim 1, wherein the pair of low voltage control
leads connect with conventional violet and gray 0-10V leads
associated with the dimmable driver.
13. The circuit of claim 1, wherein the pair of low voltage control
leads are connected with and provide the dimming control voltage to
a plurality of dimmable drivers.
14. A method for controlling the dimming level of lights in an
interior space, comprising: selectively reducing the voltage range
of the dimming control voltage to a clamped voltage range that is
less than a permissible voltage range; receiving an input current
from one or more dimmable drivers, each of the one or more dimmable
drivers electrically coupled to a respective light; detecting an
actual ambient light level in the vicinity of the lights; comparing
the detected actual ambient light level with a desired ambient
light level; setting the dimming control voltage in response to the
comparison of the detected actual ambient light level with the
desired ambient light level, wherein the dimming control voltage
must be within the selectively reduced clamped voltage range; and
providing the dimming control voltage to the one or more dimmable
drivers, the dimming control voltage determining the dimming level
of the lights.
15. The method of claim 14, wherein even with the maximum dimming
of the lights, some light is still emitted from the lights.
16. The method of claim 14, wherein the maximum dimming of the
lights causes no light to be emitted from the lights.
17. The method of claim 14, further comprising increasing the
dimming control voltage if the detected actual ambient light level
is less than the desired ambient light level.
18. The method of claim 15, wherein the clamped voltage range has a
high voltage limit set lower than the maximum output voltage and
wherein the dimming control voltage is capped at the high voltage
limit.
19. The method of claim 14, further comprising decreasing the
dimming control voltage if the detected actual ambient light level
is greater than the desired ambient light level.
20. The method of claim 19, wherein the clamped voltage range has a
low voltage limit set higher than the minimum output voltage and
wherein the dimming control voltage is capped at the low voltage
limit.
Description
I. FIELD OF THE INVENTION
[0001] The present invention relates generally to the field of
light dimming control. More particularly, the present invention
relates to controlling the dimming range of a light fixture coupled
to a dimmer.
II. BACKGROUND OF THE INVENTION
[0002] The Illuminating Engineering Society of North America
recommends a 30-50 foot-candle (fc) range for ambient (general)
office lighting, yet most workspaces are lit to 60 fc on average.
Over-lighting can cause unnecessary eye strain for occupants and
higher energy costs for companies. Under-lighting can also cause
unnecessary eye strain and provide a less pleasing or less
productive workspace.
[0003] Further, in large or open workspaces, whether the spaces are
commercial, industrial, retail, or public, such as office
buildings, warehouses, schools, malls, and the like, the amount of
light provided within the space is impacted not only by the
artificial lighting system installed in the space but also by the
amount of natural light entering the space through windows, doors,
and skylights.
[0004] However, the amount of natural light entering a space can
vary greatly based on the time of day, the time of year, and the
weather conditions at any point in time. Further, the location and
angle of the natural light entering the space can also vary greatly
based on those same factors.
[0005] Many different types of lighting-control system have been
developed to help reduce energy waste and take advantage of natural
light conditions, while still providing a productive and pleasing
visual environment. Lighting control means having the ability to
illuminate a space where and when it is needed and the power to
conserve energy when and where illumination is not needed. To
accomplish this, controls can ideally provide the right amount of
light where and when it is needed--either automatically or at a
user's discretion.
[0006] Lighting controls, such as dimming features, can reduce
lighting energy consumption and produce energy savings, especially
if the dimming is responsive to the amount of natural light
entering a space. Dimming a light fixture saves energy when
operating a light source and also allows a user to adjust the
intensity of the light source to a desired level. Many indoor and
outdoor facilities, such as homes, buildings, parking lots, and
streets, include light source dimming circuits.
[0007] The most common use of dimming is for indoor applications,
such as for dimming a room. Dimming is also ideally suited to
energy management applications, such as daylight harvesting. For
example, automated dimming systems can provide a smooth and
unnoticeable transition to lower electric light levels as daylight
levels increase, all while maintaining the desired light level, to
produce significant lighting energy savings.
[0008] For example, a time-based dimming controller can turn on a
lighting fixture at dusk, dim the lighting fixture at one or more
predetermined times to preset amounts, return the lighting fixture
to full brightness at 5 a.m., and turn off the lighting fixture at
dawn, offering 20-30 percent energy savings above normal photocell
operation.
[0009] Photo sensors can also be used to good effect to dim light
fixtures in a workspace based on detecting ambient light levels.
However, as stated above, in larger workspaces and open areas, the
amount of ambient light can vary significantly in different parts
of the workspace, based on proximity or distance from natural light
sources and based on amount of natural light coming into the
workspace at different times of the day, at different times of the
year, and based on variable weather conditions, which can change
frequently throughout a single day.
[0010] However, merely adding more photo sensors to different banks
of lights within such large workspace does not necessarily create a
pleasing or uniform lighting environment. Nor does it address the
end user's needs, which may be to have higher or lower lighting in
selected areas of the workspace.
[0011] There is thus a need to enable an end user to limit the
range and hence the dimming level of selected lighting fixtures or
banks of lights within a workspace. This is important for users who
want a more uniform "ceiling" appearance throughout the entire
workspace or who want a generally uniform ceiling appearance, but
need more customized lighting in selected areas of the workspace.
An example would be an installation with multiple photocells
installed. The fixtures near windows could be noticeably dimmer
than fixtures further away. Thus, it may be desirable for the end
user to be able to set customizable dimming or brightness levels to
keep the light level between various fixtures closer in light level
even as the ambient light level within the space varies.
[0012] These and many other needs are addressed by the circuits,
methods, devices, and systems for controlling the brightness level
of a light electrically coupled with a dimmable driver, such as a
dimming ballast or LED driver, as described in greater detail
hereinafter.
III. SUMMARY OF EMBODIMENTS OF THE INVENTION
[0013] Given the aforementioned deficiencies, a need exists for
circuits, methods, devices, and systems for controlling the
brightness level of a light electrically coupled with a dimmable
driver, such as a dimming ballast or LED driver, includes a dimming
controller that provides a dimming control voltage to the driver,
the dimming control voltage having a permissible voltage range that
is selectively reduced to a clamped dimming voltage that is less
than and contained with the permissible voltage range.
[0014] In response to the detection of the actual ambient light
level in the vicinity of the light being controlled, the dimming
control voltage is adjusted to change the brightness level of the
light to converge toward a desired ambient light level. Multiple
drivers may be controlled by a single dimming controller having a
photo sensor for detecting the actual ambient light level.
[0015] One embodiment of the present invention includes a circuit
for controlling a level of brightness of a light electrically
coupled to a dimming circuit including control leads configured to
provide a dimming control voltage to the dimmable driver, the
dimming control voltage having a permissible voltage range. The
circuit includes a photo sensor for detecting an ambient light
level in the vicinity of the light and a clamp controller for
selectively reducing the dimming control voltage to a clamped
voltage range less than the permissible voltage range. Also
included is a feedback controller for adjusting the dimming control
voltage in response to a detected ambient light level, the dimming
control voltage being within the clamped voltage range
[0016] In the embodiments, the clamped voltage range has a high
voltage limit set lower than the maximum output voltage and a low
voltage limit set higher than the minimum output voltage. The
actual ambient light level detected by the photo sensor is compared
to a desired ambient light level and the feedback controller
adjusts the dimming control voltage to adjust the level of
brightness of the light to cause the actual ambient light level to
converge toward the desired ambient light level. The desired
ambient light level is set using a reference voltage
controller.
[0017] Further features and advantages of the invention, as well as
the structure and operation of various embodiments of the
invention, are described in detail below with reference to the
accompanying drawings. It is noted that the invention is not
limited to the specific embodiments described herein. Such
embodiments are presented herein for illustrative purposes only.
Additional embodiments will be apparent to persons skilled in the
relevant art(s) based on the teachings contained herein.
IV. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The accompanying drawings, which are incorporated herein and
form part of the specification, illustrate the present invention
and, together with the description, further serve to explain the
principles of the invention and to enable a person skilled in the
relevant art(s) to make and use the invention.
[0019] FIG. 1 shows a simplified block diagram of one example
embodiment of a lighting system having a 0-10V dimmer control;
[0020] FIG. 2 shows a block diagram of the main components of an
example embodiment of a dimmer control circuit usable with the
lighting system illustrated in FIG. 1;
[0021] FIG. 3 shows a schematic diagram of the main components of
the dimmer control circuit of FIG. 2; and
[0022] FIG. 4 shows a graph of the short circuit current generated
in response to the level of ambient light detected by an exemplary
photodiode, which is usable as a component of the dimmer control
circuit of FIG. 3.
V. DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0023] While the present invention is described herein with
illustrative embodiments for particular applications, it should be
understood that the invention is not limited thereto. Those skilled
in the art with access to the teachings provided herein will
recognize additional modifications, applications, and embodiments
within the scope thereof and additional fields in which the
invention would be of significant utility.
[0024] FIG. 1 is an exemplary block diagram showing the primary
components of a lighting system 100 having dimming control. The
lighting system 100 includes a dimmable driver 50 connected between
an AC power supply 25 and an illumination load or light 90. As used
herein, and depending upon the specific lighting application, the
dimmable driver 50 is preferably either a dimming light emitting
diode (LED) driver or a dimming ballast.
[0025] As will be appreciated by those of skill in the art, the
dimming LED driver is conventionally used to drive an illumination
load 90, such as one or more LEDs or an LED array, and the dimming
ballast is conventionally used to drive a different type of
illumination load 90, such as a fluorescent light. The dimmable
driver 50 preferably includes low voltage control wires or leads
72, 74 (conventionally colored violet and gray, respectively) that
provide a low direct current (DC) voltage (e.g., 0-10V) to a dimmer
control circuit 80.
[0026] As will be explained hereinafter, the voltage (V.sub.OUT)
measured across the violet and gray low DC voltage leads or
connectors 82, 84 of the dimmer control circuit 80 is used by the
dimmable driver 50 to modify the power (typically the current, but
sometimes the output voltage) provided by the dimmable driver 50 to
the illumination load 90; thus, enabling the brightness level of
light emitted from the illumination load 90 to be controllably
dimmed between a non-dimmed, maximum (100%) output level and a
predetermined, lower, minimum output level--preferably at a level
that still emits some light and is not completely turned off.
[0027] As is conventional, the AC voltage and current from the AC
power supply 25 typically runs first through a bridge or full-wave
rectifier (not shown) and a high frequency input filter (not
shown), which filters out high frequency noise and/or
electromagnetic interference and prevents such noise or
interference from being injected back into the bridge
rectifier.
[0028] The dimmable driver 50 receives the rectified and filtered
power from the AC power supply 25 and ensures that the power
(either current or voltage) provided to the illumination load 90
does not exceed the current or voltage limits associated with the
illumination load 90. The dimmer control circuit 80 provides a
dimmer or dimming control voltage, conventionally ranging between 0
and 10V, sensed by the dimmable driver 50, which enables the light
emitted from the illumination load 90 to be dimmed in a
controllable manner by the driver 50 between full (100%)
illumination (i.e., no dimming) and a minimum, lower illumination
level (usually some percentage of dimming above 0%; otherwise, the
light is turned off completely).
[0029] Generally, for performance and energy savings reasons, it is
preferable to use an on/off switch to eliminate the light output of
illumination load 90 completely, rather than to allow the dimmer
control circuit 80 to cause the light output from the illumination
load 90 to drop below its minimum, lowest illumination level to a
zero output.
[0030] As will be described in greater detail hereinafter, the
present dimmer control circuit 80 illustrates a type of photocell
0-10V dimmer that is powered from the conventional 0-10V output
leads 72, 74 of the dimmable driver 50 (which, as used herein, is
either a dimming ballast or a dimming LED driver). Since the dimmer
control circuit 80 is powered from the 0-10V leads from the
dimmable driver 50, a separate low voltage supply (and associated
wiring) does not need to be provided.
[0031] The dimmer control circuit 80 uses a photo sensor component
to measure ambient light, which includes a combination of both
natural and artificial light sources detectable by the photo sensor
component. Preferably, the photo sensor is placed at or near the
light or illumination load 90 being controlled by its dimmable
driver 50. This ambient light measurement is continuously or
periodically compared to a desired or pre-determined light level or
set point and, based on such comparison, the dimmer control circuit
80 varies the 0-10V voltage (V.sub.OUT) of the dimmable driver 50
to maintain the output of the illumination load 90 at a desired
light level brightness regardless of fluctuations in the natural or
ambient light.
[0032] For example, as the amount of natural light increases (as
detected by the photo sensor component), the dimmable driver 50
will cause the light output of the load 90 to dim, which in turn
saves energy. Conversely, as the amount of natural light in a space
decreases, the amount of dimming decreases, eventually to a point
at which there is no dimming and the illumination load 90 is at its
full-rated brightness level.
[0033] As will be described in greater detail hereinafter, the
dimmer control circuit 80 preferably includes a selectable "ideal"
or "reference" lighting level that the tenant, building manager,
technician, automated system controller, or other end user can set
as the brightness of light (combined natural and artificial) that
the end user would like to maintain regardless of fluctuations in
the ambient or natural light detected by the photo sensor.
[0034] As will also be described in greater detail hereinafter, the
dimmer control circuit 80 preferably includes two optional clamp or
clamping circuits. These clamp circuits work independently of each
other, but can be used advantageously to limit the 0-10V dimming
range, at either or both of the low and high ends, provided to the
dimmable driver 50 by the dimmer control circuit 80. The clamp
circuits enable the end user, to limit the output voltage
(V.sub.OUT) range across the violet and gray leads and, hence,
limit the high and/or low dimming levels of the dimmable driver
50.
[0035] This dimming control for individual lights or groups of
lights is important, typically for business and commercial lighting
applications in which there is a need or desire to provide a more
uniform "ceiling" appearance or illuminated space, particularly in
a larger building or other interior space in which some lights are
closer to windows (or other natural light sources, such as
skylights, etc.) than others, which impacts the light distribution
and setting within the space. An example would be a lighting
installation with multiple photocells or photo sensors installed at
different points within the space being illuminated by a plurality
of light fixtures.
[0036] By way of example, fixtures near windows could be configured
to be noticeably dimmer than fixtures further away--particularly
during daylight hours when the amount of natural light entering the
space is likely to be greater. The clamp circuits can be used to
limit the low and high dimming levels to keep the light level
between the fixtures closer in light level, while still taking into
account the amount of ambient or natural light entering the space
at any given point or time of day.
[0037] In addition, use of window shades or blinds in some windows
could drastically affect the amount of ambient or natural light in
different locations within a single building space. Since the
clamping circuits are independent, multiple SKU products can be
offered.
[0038] For example, there can be one SKU for a dimmer control (or
dimmer control built into the ballast/LED driver) having no clamps,
another SKU can be offered that only provides low clamping
capability, another SKU can be offered that only provides high
clamping capability, or, finally, another SKU can be offered that
has both high and low clamping capability.
[0039] FIG. 2 shows a block diagram of the dimmer control circuit
80 of the example simplified system of FIG. 1 in more detail. The
dimmer control circuit 80 is comprised of the violet and gray low
DC voltage connectors 82, 84, respectively, which defines the
output voltage (V.sub.OUT) of the dimmer control circuit 80 and
which is designed to be connected to the low DC voltage leads 72.
74 from the dimmable driver 50 (as shown in FIG. 1). The dimmer
control circuit 80 preferably includes a shunt regulator circuit
210, an ambient light photo sensor and feedback circuit 220, an
error signal circuit 230, an optional upper clamp circuit 250, and
an optional lower clamp circuit 270.
[0040] In practice, the dimmable driver 50 provides a predetermined
or known input current to the dimmer control circuit 80 at the
violet low DC voltage connector 82. The dimmer control circuit 80
then adjusted its relative resistance value, based on the amount of
light detected by the photo sensor and feedback circuit 220, to
provide the desired output voltage (V.sub.OUT) across the violet
and gray low DC voltage connectors 82, 84, which determines the
amount of power (typically the current, but sometimes the output
voltage) (jgf note: refer to [0026]) provided to the illumination
load 90, which, in turn, impacts the amount of dimming, if any, of
the light output from the illumination load 90.
[0041] The optional upper and lower damp circuits 250 and 270,
respectively, determine whether the default minimum and maximum
output voltages (V.sub.OUT) (or, stated another way, the default
"range" of output voltages) that can be output by the dimmer
control circuit 80 are artificially capped, limited, or clamped to
a minimum threshold output voltage greater than the default minimum
output voltage and/or to a maximum threshold output voltage less
than the default maximum output voltage.
[0042] As will be appreciated by one of skill in the art, it is
possible for a plurality of drivers 50 to be connected
simultaneously to the dimmer control circuit 80, in such a design
configuration, the input currents provided to the dimmer control
circuit 80 at the violet low DC voltage connector 82 by all of the
plurality of drivers 50 are added together to provide a single
predetermined or known input current.
[0043] The number of drivers 50 simultaneously connected to a
single dimmer control circuit 80 will necessarily be limited by the
maximum current input parameters permitted by the specific
components, as will described with reference with FIG. 3, connected
to the violet low DC voltage connector 82.
[0044] However, for practical reasons, the number of drivers 50
connected to a single dimmer control circuit 80 will also be
limited from a practical standpoint based on the physical placement
of one or more ambient light photo sensor and feedback circuits 220
within a space to be lighted and based on how sensitive one wants
to be in controlling the dimming levels of lights or groups of
lights within a space.
[0045] Use of many ambient light photo sensor and feedback circuits
220, each connected to one or a small number of light fixtures,
allows for much finer control over the lighting levels within a
space. Conversely, using fewer ambient light photo sensor and
feedback circuits 220, each connected to a larger number of light
fixtures, would provide much less control over the lighting levels
within different areas of the same space.
[0046] Turning now to FIG. 3, a detailed schematic 300 of a
preferred embodiment of the circuitry design of the dimmer control
circuit 80 and each of its macro components, as described above
with reference to FIG. 2, is illustrated and discussed in greater
detail. As stated previously, the dimming leads 72, 74 of the
dimmable driver 50 (dimming ballast or dimming LED driver) are
labeled "violet" and "gray" and connect, respectively, with the
violet and gray low DC voltage connectors 82, 84 of the dimmer
control circuit 80.
[0047] A primary component of dimmer control circuit 80 and,
specifically of the shunt regulator circuit 210, is the shunt
regulator U1. In a preferred embodiment, the shunt regulator U1 is
a TLV431 semiconductor device, which is an exemplary low voltage,
precision, adjustable shunt regulator, manufactured and available
from numerous vendors worldwide, including Semiconductor Components
Industries, LLC based in Phoenix, Ariz., USA and having a website
at http://www.onsemi.com and Texas Instruments Incorporated based
in Dallas, Tex., USA and having a website at http://www.ti.com.
[0048] The shunt regulator U1, along with its complementary
components that make up the shunt regulator circuit 210, serves
three primary functions, including: (1) providing a maximum dimming
voltage (V.sub.OUT), (2) providing reverse polarity protection for
the dimmer control circuit 80, and (3) providing a sink for the
current from the dimming leads 72, 74. The shunt regulator U1 has
three leads or pins: an anode 302, a cathode 304, and a reference
306. The low voltage shunt regulator U1 has a built-in diode, which
protects the internal circuitry within the dimmer, from the effects
of an accidental mis-wiring at the dimming leads 72, 74.
[0049] The shunt regulator U1 "outputs" a voltage (V.sub.OUT), as
detected at cathode 304 and as detected at the violet low voltage
input 82 of the dimmer control circuit 80. The maximum output
voltage (V.sub.OUT) is controlled by the internal reference voltage
(V.sub.REF) of the shunt regulator U1 and the resistance values of
resistors R1 and R2. Low voltage shunt regulators typically have a
reference voltage of approximately 1.25V or 2.5V. Preferably, and
as used herein, the shunt regulator U1 has a reference voltage of
approximately 1.25V to provide a low voltage output close to, but
slightly above, 0V. The ideal equation (Equation 1) for determining
the maximum output voltage (V.sub.OUT) for the low voltage shunt
regulator U1 is defined by:
V.sub.OUT=V.sub.REF*(1+R1/R2)
[0050] Thus, with a known voltage reference (V.sub.REF) and a
desired maximum output voltage (V.sub.OUT), the values of resistors
R1 and R2 can be chosen to set the desired maximum output voltage
(V.sub.OUT) that can be provided by the dimming control circuit 80
back to the dimmable driver 50. In a preferred embodiment, the
values of R1 and R2 are chosen so that the maximum output voltage
(V.sub.OUT) generated by the above Equation 1 is approximately
10V.
[0051] The minimum output voltage (V.sub.OUT) will be approximately
the same as the voltage reference (V.sub.REF), which in this case
is 1.25V, for reasons that will be now explained. Specifically,
although it is possible to modify the output voltage dynamically by
varying the resistance values of R1 and/or R2, the preferred system
described herein keeps resistors R1 and R2 at their predetermined,
fixed resistance values and, instead, modifies the injection
current (I.sub.INJ) feeding into the node between resistors R1 and
R2, which represents the variable current flowing from the
collector 312 of transistor Q1 into the reference pin 306 of the
shunt regulator U1. The ideal equation (Equation 2) for determining
the "actual" output voltage (V.sub.OUT) for the low voltage shunt
regulator U1 based on the variable injection current (I.sub.INJ) is
defined by:
V.sub.OUT=V.sub.REF*(1+R1/R2)-(I.sub.INJ*R1)
[0052] Thus, as can be readily determined, if the injection current
(I.sub.INJ) is zero, the output voltage (V.sub.OUT) from the shunt
regulator U1 is at its maximum value, having the same value as
determined from Equation 1. However, as the injected current
(I.sub.INJ) increases, the output voltage (V.sub.OUT) of the shunt
regulator U1 decreases down toward its minimum value, as set by the
reference voltage (V.sub.REF).
[0053] With reference back to the ambient light photo sensor and
feedback circuit 220 from FIG. 2, such ambient light photo sensor
and feedback circuit 220 includes a light sensitive device or photo
sensor 320, such as the silicon photodiode D1 available under the
semiconductor component name BPW21R, which is manufactured and
available from numerous vendors, including Vishay Intertechnology,
Inc. based in Malvern, Pa., USA and having a website at
http://www.vishay.com.
[0054] This photodiode D1 outputs a current (I.sub.K) that is
substantially linearly-correlated to the ambient and natural light
levels (E.sub.A) detected by the integrated photo sensor of the
photodiode D1, as shown by the line 405 on graph 400 in FIG. 4.
Thus, the current (I.sub.K) generated by the photodiode D1
increases as the ambient and natural light detected by the
photodiode D1 increases.
[0055] The current mirror 330 provides the required short circuit
for photodiode D1, and the injection current (I.sub.INJ) required
by the dimmer control circuit 80. The current mirror 330 includes
resistors R3 and R4, transistors Q2 and Q3, and the above-described
photodiode D1. The current (I.sub.K) generated by photodiode D1
causes a current to flow in transistor Q2, which, based on the
configuration of the current mirror 330, causes a corresponding
mirror current to flow in the collector 332 of transistor Q3.
[0056] The current flowing from the collector 332 of transistor Q3
represents a feedback current, which varies based on the amount of
light detected by photodiode D1, as explained above. This feedback
current flows through calibration resistor R7, which establishes a
feedback voltage that is detected at the input into the negative
(-) or inverting terminal 342 of operational amplifier (op amp) U2.
Preferably, calibration resistor R7 is a variable resistor that
will typically be calibrated at the factory, and not by an end user
of the dimmer control circuit 80, to account for any slight
variations or errors in the light sensor of the photodiode D1.
[0057] A reference voltage is provided to the positive (+) or
non-inverting terminal 344 of operational amplifier (op amp) U2.
This reference voltage correlates to and establishes the "ideal" or
"reference" lighting level desired by the end user and that the end
user would like to maintain regardless of fluctuations in the
ambient or natural light detected by the photodiode D1. This
reference voltage at terminal 344 is controlled by a reference
voltage circuit, which includes resistors R3, R9, R10, shunt
voltage regulator VR1, and capacitor C6. Resistor R9 is a variable
resistor that enables the user to adjust the reference voltage
provided to the non-inverting terminal 344 of op amp U2.
[0058] The voltage drop across resistor R9 is variable, but falls
within a predefined range based on the resistance range of variable
resistor R9 and the selected resistance value of resistor
R10--wherein resistor R9 and resistor R10 together create a
conventional voltage divider. Resistor R8 is used as a bias
resistor to prevent too much current from overloading the shunt
voltage regulator VR1. Shunt voltage regulator VR1 regulates the
voltage range across resistors R8 and R9. Preferably, the reference
voltage for shunt voltage regulator VR1 needs to be at (or lower
than) the reference voltage of shunt regular U1. Thus, in this
preferred embodiment, the reference voltage of VR1 is set to 1.25V
(or less), since the reference voltage of shunt regulator U1 is set
at 1.25V.
[0059] Thus, op amp U2 detects and compares the two input voltages:
(i) the feedback voltage provided to the negative (-) or inverting
terminal 342 (which fluctuates based on the amount of light
detected by the photo sensor) and the reference voltage provided to
the positive (+) or non-inverting terminal 344 (which represents
the user-desired lighting level). In operation, the reference
voltage provided to the positive (+) or non-inverting terminal 344
generally remains constant. The feedback voltage provided to the
negative (-) or inverting terminal 342, however, will vary as the
ambient light varies. Feedback components, including resistor R6
and capacitor C4, are adjusted and used for stability purposes.
[0060] Therefore, in operation, if the photodiode D1 detects very
little to no ambient light, the feedback current flowing from the
collector 332 of transistor Q3 is zero or otherwise very small,
which causes the feedback voltage at the inverting terminal 342 to
be lower than the reference voltage at the non-inverting terminal
344, which causes the output 346 of op amp U2 to go high, which
drives the base 314 of transistor Q1 which, in turn, causes the
injection current (I.sub.INJ) from the collector 312 of transistor
Q1 flowing into the node between resistors R1 and R2 to reduce
toward zero, which causes the output voltage (V.sub.OUT) from the
shunt regulator U1 is go toward its maximum value, as determined
from Equation 1 and Equation 2, which increases the light output of
the illumination load 90.
[0061] On the other hand, as the photodiode D1 detects more and
more ambient light, the feedback current flowing from the collector
332 of transistor Q3 increases, which causes the feedback voltage
at the inverting terminal 342 gradually to increase. When the
feedback voltage exceeds the reference voltage detected at the
non-inverting terminal 344, the output 346 of op amp U2 goes
low.
[0062] The amp U2 going low drives the base 314 of transistor Q1
and causes the injection current (I.sub.INJ) from the collector 312
of transistor Q1 flowing into the node between resistors R1 and R2
to increase. This increase causes the output voltage (V.sub.OUT)
from the shunt regulator U1 is go toward its minimum value, as
determined from Equation 1 and Equation 2.
[0063] Consequently, the dimmable driver 50 to begins dimming the
light output from the illumination load 90, which makes sense based
on the fact that ambient light is being detected and the light
output from the illumination load 90 can be decreased to save
energy and to maintain the light levels in the illuminated space at
a more uniform level even as the amount of ambient light
increases.
[0064] The upper and lower clamping circuits 250 and 270 can be
used to modify the level of injection current (I.sub.INJ) flowing
into the shunt regulator U1. This artificially caps the maximum
output voltage (V.sub.OUT) provided by the dimmer control circuit
80 to the dimmable driver 50 to below 10V. Consequently, the
illumination load 90 begins to dim even if there is no or very
little detectable ambient light.
[0065] Modification of the level of injection current (I.sub.INJ)
flowing into the shunt regulator U1 also artificially raises the
minimum output voltage (V.sub.OUT) provided by the dimmer control
circuit 80 to the dimmable driver 50 to above its minimum reference
voltage of 1.25V, which reduces the dimming of the illumination
load 90 even when there is a higher level of detectable ambient
light.
[0066] As described above, the feedback current flowing from the
collector 332 of transistor Q3 and through calibration resistor R7
is used to calculate a feedback voltage corresponding to the amount
of ambient light being detected, which can then be compared by op
amp U2 with a reference voltage that is established, based on the
desired light level selected by the end user, by varying the
resistance of resistor R9. A damping current can be used to modify
the feedback current, having either a subtractive or additive
effect on the feedback current at node 338, if the dimmer control
circuit 80 includes either (or both) of the optional upper and
lower clamp circuits 250 and 270, as will be described in greater
detail hereinafter.
[0067] In addition to regulating the voltage range across resistors
R8 and R9, shunt voltage regulator VR1 provides a reference voltage
and is connected to the positive (+) or non-inverting terminals of
op amps U3A and U3B. As stated previously, the reference voltage
for shunt voltage regulator VR1 needs to be at (or lower than) the
reference voltage of shunt regulator U1. Thus, in this preferred
embodiment, the reference voltage of VR1 is set to 1.25V (or less),
since the reference voltage of shunt regulator U1 is set at
1.25V.
[0068] The low clamp circuit 270 includes op amp U3B, resistors
R21, R22, R23, R29 and R30, capacitor C21, and transistor Q21.
Resistor R23 is adjustable by the end user to establish a low
voltage set point. The low voltage set point can range from a low
of 1.25V (i.e., the reference voltage of shunt regulator U1) to an
arbitrary high of X.sub.H volts, for reasons that will become
apparent. Thus, as the voltage output (V.sub.OUT) of the dimmer
control circuit 80 lowers toward the low voltage set point, the
output of op amp U3B will increase and the base current 364 of
transistor Q21 will increase. This will cause the collector current
362 of Q21 to increase and "steal" or siphon off some of the
feedback current flowing from the collector 332 of transistor
Q3.
[0069] As stated above, this has a subtractive effect on the
feedback current at node 338. This causes the output voltage
(V.sub.OUT) to rise and stay above the low voltage set point. The
output of op amp U3B will vary to keep the light level at the
desired low set point.
[0070] The high clamp circuit 250 includes op amp U3A, resistors
R24, R25, R26, R27, and R28, capacitor C22, and transistor Q20.
Resistor R26 is adjustable by the end user to establish a high
voltage set point. The high voltage set point can range from a high
of 10V the maximum output voltage of shunt regulator U1) to an
arbitrary low of X.sub.L volts, for reasons that will become
apparent. Thus, as the voltage output (V.sub.OUT) of the dimmer
control circuit 80 rises toward the high voltage set point, the
output of op amp U3A will decrease and the base current 374 of
transistor Q20 will increase. This will cause the collector current
372 of Q20 to increase and "inject" or feed more current into the
feedback current flowing from the collector 332 of transistor Q3.
As stated above, this has an additive effect on the feedback
current at node 338. This causes the output voltage (V.sub.OUT) to
decrease and stay below the high voltage set point. The output of
op amp U3A will vary to keep the light level at the desired high
set point.
[0071] Because both transistors Q20 and Q21 connect into the
feedback current flowing from the collector 332 of transistor Q3 at
node 338, it will be apparent to one of skill in the art that it is
not desirable to have both transistors Q20 and Q21 feeding or
drawing current at node 338 at the same time. To avoid this
conflict, if the dimmer control circuit 80 makes use of both the
high and low clamp circuits 250, 270, it is necessary that the
arbitrary high voltage X.sub.H set by the low clamp circuit 270 be
lower than the arbitrary low voltage X.sub.L set by the high clamp
circuit 250.
[0072] Even though the voltage levels for the arbitrary high and
low voltages X.sub.H and X.sub.L could be close to each other,
doing so would not make much practical sense because that would
effectively limit the dimming range of the dimmer control circuit
80. Conversely, if the dimmer control circuit 80 has either the
high or low clamp circuit 250, 270, but not both, then there is no
worry about having an overlap between the arbitrary high and low
voltages X.sub.H and X.sub.L. However, it will also be appreciated
by those of skill in the art that, in order for the either the high
or low clamp circuits 250, 270 to have any impact, their set point
voltages will still have to be set to a level somewhere between the
minimum and maximum output voltages of the shunt regulator U1,
which, in this case, is between 1.25V and 10V.
CONCLUSION
[0073] Embodiments of the present invention include a circuit for
controlling a level of brightness of a light electrically coupled
to a dimming circuit including control leads configured to provide
a dimming control voltage to the dimmable driver, the dimming
control voltage having a permissible voltage range. The circuit
includes a photo sensor for detecting an ambient light level in the
vicinity of the light and a clamp controller for selectively
reducing the dimming control voltage to a clamped voltage range
less than the permissible voltage range. Also included is a
feedback controller for adjusting the dimming control voltage in
response to a detected ambient light level, the dimming control
voltage being within the clamped voltage range.
[0074] The present invention has been described above with the aid
of functional building blocks illustrating the implementation of
specified functions and relationships thereof. The boundaries of
these functional building blocks have been arbitrarily defined
herein for the convenience of the description. Alternate boundaries
can be defined so long as the specified functions and relationships
thereof are appropriately performed.
[0075] For example, various aspects of the present invention can be
implemented by software, firmware, hardware (or hardware
represented by software such, as for example, Verilog or hardware
description language instructions), or a combination thereof. After
reading this description, it will become apparent to a person
skilled in the relevant art how to implement the invention using
other computer systems and/or computer architectures.
[0076] It is to be appreciated that the Detailed Description
section, and not the Summary and Abstract sections, is intended to
be used to interpret the claims. The Summary and Abstract sections
may set forth one or more, but not all, exemplary embodiments of
the present invention as contemplated by the inventor(s), and thus,
are not intended to limit the present invention and the appended
claims in any way.
* * * * *
References