Patent Grant
10057952
The inventive subject matter relates to lighting apparatus and methods of operation thereof and, more particularly, to apparatus and methods for control of lighting apparatus.
Solid state lighting devices are used for a number of lighting applications. For example, solid state lighting panels including arrays of solid state light emitting devices have been used as direct illumination sources, for example, in architectural and/or accent lighting. A solid state light emitting device may include, for example, a packaged light emitting device including one or more light emitting diodes (LEDs). Inorganic LEDs typically include semiconductor layers forming p-n junctions. Organic LEDs (OLEDs), which include organic light emission layers, are another type of solid state light emitting device. Typically, a solid state light emitting device generates light through the recombination of electronic carriers, i.e. electrons and holes, in a light emitting layer or region.
In many solid-state lighting applications, current is driven through an arrangement of LEDs to obtain a certain light output. This current is typically sensed to provide feedback to a controller that controls the level of illumination and/or color point.
Current sense resistors may also be used in color point control applications. The color rendering index (CRI) of a light source is an objective measure of the ability of the light generated by the source to accurately illuminate a broad range of colors. The color rendering index ranges from essentially zero for monochromatic sources to nearly 100 for incandescent sources. Light generated from a phosphor-based solid state light source may have a relatively low color rendering index.
It is often desirable to provide a lighting source that generates a white light having a high color rendering index, so that objects and/or display screens illuminated by the lighting panel may appear more natural. Accordingly, to improve CRI, red light may be added to the white light, for example, by adding red emitting phosphor and/or red emitting devices to the apparatus. Other lighting sources may include red, green and blue light emitting devices. When red, green and blue light emitting devices are energized simultaneously, the resulting combined light may appear white, or nearly white, depending on the relative intensities of the red, green and blue sources.
In some applications, the color point of an LED lighting apparatus may be controlled by controlling currents flowing through different color LEDs of the apparatus. For example, U.S. patent application Ser. No. 12/704,730, entitled “SOLID STATE LIGHTING APPARATUS WITH COMPENSATION BYPASS CIRCUITS AND METHODS OF OPERATION THEREOF,” filed Feb. 12, 2010, describes bypass circuits configured to selectively bypass current around light emitting devices of a serially-connected string of light emitting devices to achieve, for example, color point control. Such bypass circuits may operate responsive to a voltage developed across a current sense resistor connected in series with the string of light emitting devices, such that a desired color point may be maintained in response to, for example, variations in string current caused by a dimming circuit.
A lighting apparatus according to some embodiments of the inventive subject matter includes a lighting circuit including at least one light-emitting device and at least one current sense diode configured to generate a forward voltage responsive to a current passing through the at least one light-emitting device. The apparatus further includes a control circuit configured to control the lighting circuit responsive to the generated forward voltage. In some embodiments, the least one light-emitting device includes the at least one current sense diode.
In further embodiments, the lighting circuit includes a string of serially connected light emitting devices and the at least one current sense diode is connected in series with serially connected light emitting devices. In some embodiments, the control circuit may be configured to control a current passing through the string of serially connected light emitting devices responsive to the sensed forward voltage. In some embodiments, the control circuit may be configured to control a bypass current around at least one light emitting device of the string of serially connected light emitting devices responsive to the sensed forward voltage.
According to further embodiments, the lighting circuit may include a first string of serially connected light emitting devices and a second string of serially connected light emitting devices, and the current sense diode may be connected in series with the first string of serially connected light emitting devices. The control circuit may be configured to control a current through the second string of serially connected light emitting devices responsive to the sensed forward voltage.
In additional embodiments, the apparatus further includes a temperature sensor configured to generate a temperature sense signal. The control circuit may be configured to control the lighting apparatus responsive to the forward voltage and the temperature sense signal.
According to some embodiments, the at least one current sense diode includes at least one LED. The lighting circuit may include a string of serially connected LEDs and the at least one current sense diode may be connected in series with the string of serially connected LEDs. In some embodiments, the at least one current sense diode may be an LED of the string of serially connected LEDs. In some embodiments, the control circuit may be configured to control a current passing through the string of serially connected LEDs responsive to the sensed forward voltage. In some embodiments, the control circuit may be configured to control a bypass current around at least one LED of the string of serially connected LEDs responsive to the sensed forward voltage.
In additional embodiments, the lighting circuit may include a first string of serially connected LEDs and a second string of serially connected LEDs. The current sense diode may include at least one LED of the first string of serially connected LEDs. The control circuit may be configured to control a current through the second string of serially connected LEDs responsive to the sensed forward voltage. The first and second strings of serially connected LEDS may include LEDs of different colors.
According to further embodiments of the inventive subject matter, a lighting apparatus includes at least one string of serially connected LEDs and at least one current sense diode configured to generate a forward voltage responsive to a current passing through the at least one string of serially connected LEDs. The apparatus further includes a control circuit configured to sense the forward voltage and to control the at least one string of LEDs responsive to the sensed forward voltage. The at least one current sense diode may include at least one LED of the string of serially connected LEDs.
In some embodiments, the control circuit may be configured to control a current passing through the string of serially connected LEDs responsive to the sensed forward voltage. In further embodiments, the control circuit may be configured to control a bypass current around at least one LED of the string of serially connected LEDs responsive to the sensed forward voltage.
In still further embodiments, the at least one string of serially connected LEDs may include a first string of serially connected LEDs and a second string of serially connected LEDs. The current sense diode may be connected in series with the first string of serially connected LEDs and the control circuit may be configured to control a current through the second string of serially connected LEDs responsive to the sensed forward voltage. The first and second strings of serially connected LEDS may include LEDs of different colors.
In additional embodiments of the inventive subject matter, a lighting apparatus includes a lighting circuit including at least one light-emitting device. The apparatus further includes a non-linear current sensor configured to generate a voltage representative of a current passing through the at least one light-emitting device and a control circuit configured to control the lighting circuit responsive to the generated voltage. The current may have a substantially exponential relationship the generated voltage. For example, the non-linear current sensor may include a diode and the voltage may be a forward voltage across the diode.
In some method embodiments, a lighting circuit including at least one light-emitting device is controlled. A forward voltage is generated across at least one current sense diode responsive to a current passing through the at least one light-emitting device. The forward voltage is sensed and the lighting circuit is controlled responsive to the sensed forward voltage. The at least one light-emitting device may include the at least one current sense diode. The at least one current sense diode may include at least one LED. For example, the lighting circuit may include a string of serially connected LEDs and the at least one current sense diode may be connected in series with the string of serially connected LEDs and/or may include at least one of the LEDs.
The accompanying drawings, which are included to provide a further understanding of the inventive subject matter and are incorporated in and constitute a part of this application, illustrate certain embodiment(s) of the inventive subject matter.
FIG. illustrates lighting apparatus and calibration apparatus therefore according to further embodiments of the inventive subject matter.
Embodiments of the inventive subject matter now will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the inventive subject matter are shown. This inventive subject matter may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive subject matter to those skilled in the art. Like numbers refer to like elements throughout.
It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the inventive subject matter. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
It will be understood that when an element such as a layer, region or substrate is referred to as being “on” or extending “onto” another element, it can be directly on or extend directly onto the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” or extending “directly onto” another element, there are no intervening elements present. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the inventive subject matter. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” “comprising,” “includes” and/or “including” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this inventive subject matter belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. The term “plurality” is used herein to refer to two or more of the referenced item.
The lighting apparatus 10 generally includes a can shaped outer housing 12 in which a lighting panel 20 is arranged. In the embodiments illustrated in
Still referring to
The chromaticity of a particular light source may be referred to as the “color point” of the source. For a white light source, the chromaticity may be referred to as the “white point” of the source. The white point of a white light source may fall along a locus of chromaticity points corresponding to the color of light emitted by a black-body radiator heated to a given temperature. Accordingly, a white point may be identified by a correlated color temperature (CCT) of the light source, which is the temperature at which the heated black-body radiator matches the hue of the light source. White light typically has a CCT of between about 2500K and 8000K. White light with a CCT of 2500K has a reddish color, white light with a CCT of 4000K has a yellowish color, and while light with a CCT of 8000K is bluish in color.
“Warm white” generally refers to white light that has a CCT between about 3000 and 3500° K. In particular, warm white light may have wavelength components in the red region of the spectrum, and may appear yellowish to an observer. Incandescent lamps are typically warm white light. Therefore, a solid state lighting device that provides warm white light can cause illuminated objects to have a more natural color. For illumination applications, it is therefore desirable to provide a warm white light. As used herein, white light refers to light having a color point that is within 7 MacAdam step ellipses of the black body locus or otherwise falls within the ANSI C78-377 standard.
In order to achieve warm white emission, conventional packaged LEDs include either a single component orange phosphor in combination with a blue LED or a mixture of yellow/green and orange/red phosphors in combination with a blue LED. However, using a single component orange phosphor can result in a low CRI as a result of the absence of greenish and reddish hues. On the other hand, red phosphors are typically much less efficient than yellow phosphors. Therefore, the addition of red phosphor in yellow phosphor can reduce the efficiency of the package, which can result in poor luminous efficacy. Luminous efficacy is a measure of the proportion of the energy supplied to a lamp that is converted into light energy. It is calculated by dividing the lamp's luminous flux, measured in lumens, by the power consumption, measured in watts.
Warm white light can also be generated by combining non-white light with red light as described in U.S. Pat. No. 7,213,940, entitled “LIGHTING DEVICE AND LIGHTING METHOD,” which is assigned to the assignee of the inventive subject matter, and the disclosure of which is incorporated herein by reference. As described therein, a lighting device may include first and second groups of solid state light emitters, which emit light having dominant wavelength in ranges of from 430 nm to 480 nm and from 600 nm to 630 nm, respectively, and a first group of phosphors which emit light having dominant wavelength in the range of from 555 nm to 585 nm. A combination of light exiting the lighting device which was emitted by the first group of emitters, and light exiting the lighting device which was emitted by the first group of phosphors produces a sub-mixture of light having x, y color coordinates within a defined area on a 1931 CIE Chromaticity Diagram that is referred to herein as “blue-shifted yellow” or “BSY.” Such non-white light may, when combined with light having a dominant wavelength from 600 nm to 630 nm, produce warm white light.
Blue and/or green LEDs used in a lighting apparatus according to some embodiments may be InGaN-based blue and/or green LED chips available from Cree, Inc., the assignee of the inventive subject matter. Red LEDs used in the lighting apparatus may be, for example, AlInGaP LED chips available from Epistar, Osram and others.
In some embodiments, the LEDs 22, 24 may have a square or rectangular periphery with an edge length of about 900 μm or greater (i.e. so-called “power chips.” However, in other embodiments, the LED chips 22, 24 may have an edge length of 500 μm or less (i.e. so-called “small chips”). In particular, small LED chips may operate with better electrical conversion efficiency than power chips. For example, green LED chips with a maximum edge dimension less than 500 microns and as small as 260 microns, commonly have a higher electrical conversion efficiency than 900 micron chips, and are known to typically produce 55 lumens of luminous flux per Watt of dissipated electrical power and as much as 90 lumens of luminous flux per Watt of dissipated electrical power.
The LEDs 22 in the lighting apparatus 10 may include white/BSY emitting LEDs, while the LEDs 24 in the lighting apparatus may emit red light. Alternatively or additionally, the LEDs 22 may be from one color bin of white LEDs and the LEDs 24 may be from a different color bin of white LEDs. The LEDs 22, 24 in the lighting apparatus 10 may be electrically interconnected in one or more series strings, as in embodiments of the inventive subject matter described below. While two different types of LEDs are illustrated, other numbers of different types of LEDs may also be utilized. For example, red, green and blue (RGB) LEDs, RGB and cyan, RGB and white, or other combinations may be utilized.
Some embodiments of the inventive subject matter arise from a discovery that non-linear current sensors may be advantageously used to control a lighting circuit, such as a string of LEDs. According to some embodiments, a non-linear, low-dissipation current sensor for lighting circuits may take the form of one or more diodes, which may have characteristics that are particularly suitable for controlling LED lighting devices. In some embodiments, the current sensing diode(s) may be one of the illuminating LEDs of the lighting apparatus.
A color of light produced by combining two or more different colors of LEDs may drift with variations in current passing through the LEDs. For example, if a lighting apparatus containing one or more strings of LEDs of different colors is dimmed by reducing the current flowing therethrough, different light output vs. current characteristics of the different color LEDs may cause a variation in the color point of the apparatus. Such variation may become problematic at low intensities, as the human eye is generally more sensitive to small variations at lower intensity levels.
A voltage-current (V-I) curve of an ideal diode may be given by:
I=ISeV/V
where IS is the diode's reverse saturation current, V is the forward voltage across the diode and VT is the thermal voltage of the diode. The voltage across the diode can be expressed as a logarithmic function of the current I through the diode:
V=VT ln(I/IS). (2)
Some embodiments of the inventive subject matter may take advantage of this characteristic by using a diode as a non-linear current sensor that provides a substantially logarithmic current feedback signal that provides different gains at different current levels. As the thermal voltage VT of a diode may vary with temperature, some embodiments may provide more consistently effectively logarithmic feedback over a range of temperatures by compensating for temperature responsive to a temperature sense signal. In some embodiments, compensation for non-ideal diode behavior arising from, for example, leakage current and series resistance, may also be provided. In some embodiments, for example, a microcontroller may implement a lookup table that provides temperature and other compensation and/or a response function (e.g. a polynomial) that includes parameters that account for temperature and deviation of diode behavior from ideal logarithmic performance. Such lookup tables and/or response parameters may be generated, for example, in a calibration procedure.
Such a compensation function may be, for example, a linear model based on a datasheet value for change in forward voltage of a current sensing diode with temperature. Higher order models may also be used. For example, a bicubic surface polynomial or Bezier patch might be used for a compensation and/or response function. Such models may be used, for example, to generate an explicit representation of current or to generate a control signal that implicitly includes temperature-compensated current feedback information. For example, temperature and current data may be fed into such a function and used to generate, for example, a duty cycle command for a PWM circuit that controls current through a string of LEDs. Such models may be generated, for example, by generating data while operating the controlled lighting apparatus over temperature, current and dimming ranges and using a linear regression to determine model parameters, e.g., polynomial coefficients.
As illustrated in
In some embodiments, a current sensing diode may be used to sense a current passing through a string of LEDs and used to control a current though the string. For example, as illustrated in
It will be appreciated that the current sense diode 420 may be one or more LEDs of the LED string 410, one or more non-light emitting diodes or a combination thereof. The current sense diode 420 could also be connected in a different serial arrangement, for example, the current sense diode 420 could be connected in the middle of the string 410 and a differential voltage across the current sense diode 420 could be provided to the control circuit 430. Other current control arrangements may also be used. For example, as shown in
As shown in
The control circuit 640 may be implemented using any of a variety of digital and/or analog control circuits. For example, as shown in
The microcontroller 742 may be programmed to perform temperature compensation for the current feedback signal Vsense. For example, as shown in
In some embodiments, similar functionality may be provided using analog circuitry instead of a microcontroller. For example, as illustrated in
According to further embodiments of the inventive subject matter, a diode current sensor may be employed with a controllable bypass circuit that is used to selectively bypass current around one or more LEDs of a string for purposes of, for example, color control. The aforementioned U.S. patent application Ser. No. 12/704,730, entitled “SOLID STATE LIGHTING APPARATUS WITH COMPENSATION BYPASS CIRCUITS AND METHODS OF OPERATION THEREOF,” filed Feb. 12, 2010 and incorporated herein by reference in its entirety, describes the use of controllable bypass circuits lighting apparatus. According to some embodiments of the inventive subject matter, such bypass circuits may be modified to utilize non-linear current sensors to provide advantageous performance.
For example, a lighting apparatus 1000 illustrated in
In additional embodiments illustrated in
In the drawings and specification, there have been disclosed typical embodiments of the inventive subject matter and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the inventive subject matter being set forth in the following claims.
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