LED lighting devices configured to produce a halogen-like dimming effect

Abstract

A lighting device is provided. The lighting device includes a first plurality of white LEDs, a second plurality of white LEDs, one or more third LEDs, a driver, and a switching circuit. Each of the first plurality of white LEDs has a first CCT. Each of the second plurality of white LEDs has a second CCT. The first CCT is greater than the second CCT. The one or more third LEDs arranged in series with the second plurality of white LEDs. The driver is configured to provide an output current to the first plurality of white LEDs or the second plurality of white LEDs according to a dimming factor. The switching circuit is configured to direct the output current to either the first plurality of white LEDs or the second plurality of white LEDs based on a current sensing signal. Further, a bypass circuit may be used to activate or bypass the one or more third LEDs.

Description

[0001] LED LIGHTING DEVICES CONFIGURED TO PRODUCE A HALOGEN-LIKE

[0002] DIMMING EFFECT

[0003] FIELD OF THE INVENTION

[0004] The present disclosure is generally directed to dimmable LED lighting devices, and, more particularly, to LED lighting devices configured to produce a halogen-like dimming effect.

[0005] BACKGROUND OF THE INVENTION

[0006] Incandescent halogen lighting devices have a wide correlated color temperature (CCT) range while dimming. In some examples, the CCT of the incandescent halogen lighting devices may range from approximately 3000K to under 1400K. As light emitting diodes (LEDs) are replacing halogen bulbs in modern lighting devices, there is a need to recreate the dimming effect of halogen incandescent lighting devices using LEDs. Some existing lighting devices implement a microcontroller and a look-up table to blend different types of LEDs generating different CCTs to produce the desired dimming effect. Another lighting device described in US Patent No. 9,730,291 has a light source with two groups of LEDs, each group having different CCT values, and a differential amplifier to adjust a current flow through the second of the two groups of LEDs, where the second group of LEDs is switched on when a current to the light source is detected by a current sensor to be below a threshold. However, there is a need in the art for a better solution to provide the dimming effect of incandescent halogen lighting devices with the required black body curve correction.

[0007] SUMMARY OF THE INVENTION

[0008] The present disclosure is generally directed to a lighting device configured to produce a halogen-like dimming effect using light emitting diodes (LEDs). The lighting device includes a first plurality of white LEDs, a second plurality of white LEDs, and one or more third LEDs. The second plurality of white LEDs are arranged in series with the one or more third LEDs, while the first plurality of white LEDs are arranged in parallel with the second plurality of white LEDs and the one or more third LEDs. The first plurality of white LEDs have a higher correlated color temperature (CCT) than the second plurality of white LEDs. For example, the first plurality of white LEDs may each have a CCT of approximately 3000K, while the second plurality of white LEDs may each have a CCT of approximately 1400K. The one or more third LEDs include at least one amber LED and / or at least one lime LED. A driver generates a dimmable output current based on a dimming factor. A switching circuit then directs the output current to either the first or second plurality of white LEDs according to a current sensing signal based on the output current of the driver. Rapidly switching (at a rate faster than 24 Hz) between the two types of white LEDs effectively blends the output light of the white LEDs together, enabling the halogen-like dimming effect, while the amber and / or lime LEDs of the one or more third LEDs provide black body curve correction.

[0009] The switching circuit can include a pulse width modulation (PWM) signal generator. The PWM signal generator generates a PWM control signal based on the current sensing signal. In particular, the PWM control signal has a duty cycle proportional to the dimming factor. The PWM signal is provided to a switch coupled to the first plurality of white LEDs. The total forward voltage of the first plurality of white LEDs is configured to be lower than the total forward voltage of the second plurality of white LEDs. The switch closes when the PWM signal is high, enabling the output current to flow through the first plurality of white LEDs due to its lower total forward voltage. When the PWM signal is low, the switch opens, diverting the output current through the second plurality of white LEDs and the one or more third LEDs. Further, a bypass circuit may be used to activate or bypass the one or more third LEDs. The current sensing signal may also be provided to a window comparator to determine if the dimming factor is within a dimming window. If the dimming factor is outside of the dimming window, the amber LEDs and / or lime LEDs are not required for black body curve correction, and the switching circuit bypasses the one or more third LEDs.

[0010] Generally, a lighting device is provided. The lighting device includes a first plurality of white LEDs. Each of the first plurality of white LEDs has a first correlated color temperature (CCT).

[0011] The lighting device further includes a second plurality of white LEDs. Each of the second plurality of white LEDs has a second CCT. The first CCT is greater than the second CCT.

[0012] The lighting device further includes one or more third LEDs arranged in series with the second plurality of white LEDs. The lighting device further includes a driver. The driver is configured to provide an output current to the first plurality of white LEDs or the second plurality of white LEDs according to a dimming factor.

[0013] The lighting device further includes a switching circuit. The switching circuit is configured to direct the output current to either the first plurality of white LEDs or the second plurality of white LEDs based on a current sensing signal.

[0014] In some embodiments, the first CCT is approximately 3000K.

[0015] In some embodiments, the second CCT is approximately 1400K.

[0016] In some embodiments, the first plurality of white LEDs comprises two or more parallel strings of white LEDs. In some embodiments, each of the two or more parallel strings comprises an equal number of white LEDs.

[0017] In some embodiments, the first plurality of white LEDs are arranged in parallel with the second plurality of white LEDs and the one or more third LEDs.

[0018] In some embodiments, the one or more third LEDs comprise at least one amber LED and / or at least one lime LED.

[0019] In some embodiments, a first total forward voltage of the first plurality of white LEDs is less than a second total forward voltage of the second plurality of white LEDs.

[0020] In some embodiments, if the dimming factor is 100%, the second plurality of white LEDs and the one or more third LEDs are deactivated.

[0021] In some embodiments, the switching circuit comprises a PWM signal generator configured to generate a PWM control signal configured to control the first plurality of white LEDs. The PWM control signal is generated based on the current sensing signal.

[0022] In some embodiments, a duty cycle of the PWM control signal is proportional to the dimming factor.

[0023] In some embodiments, a switching frequency of the PWM control signal is at least 24 Hz.

[0024] In some embodiments, the lighting device further includes a bypass circuit.

[0025] The bypass circuit is configured activate the one or more third LEDs according to the output current.

[0026] In some embodiments, the bypass circuit further includes a window comparator coupled to the bypass circuit. The bypass circuit activates the one or more third LEDs based on the current sensing signal and a dimming window of the window comparator. In some embodiments, the lighting device comprises three of the second plurality of white LEDs for every one of the one or more third LEDs.

[0027] It should be appreciated that all combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutually inconsistent) are contemplated as being part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are contemplated as being part of the inventive subject matter disclosed herein. It should also be appreciated that terminology explicitly employed herein that also may appear in any disclosure incorporated by reference should be accorded a meaning most consistent with the particular concepts disclosed herein.

[0028] These and other aspects of the various embodiments will be apparent from and elucidated with reference to the embodiment s) described hereinafter.

[0029] BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the various embodiments.

[0031] Fig. 1 is a schematic of a dimmable LED lighting device, in accordance with an example.

[0032] Fig. 2 is a plot of currents of two types of LEDs of a lighting device along a dimming range, in accordance with an example.

[0033] Fig. 3 is a plot of correlated color temperature produced by a dimmable LED lighting device, in accordance with an example.

[0034] Fig. 4 is a plot of a black body curve and four types of LEDs, in accordance with an example.

[0035] Fig. 5 is a plot of currents of three types of LEDs of a lighting device along a dimming range including LEDs for black body curve correction, in accordance with an example.

[0036] Fig. 6 is a plot of calculated and approximated currents for powering LEDs for black body correction, in accordance with an example.

[0037] Fig. 7 is a plot of correlated color temperature produced by a dimmable LED lighting device implementing black body curve correction, in accordance with an example. DETAILED DESCRIPTION OF EMBODIMENTS

[0038] The present disclosure is generally directed to a lighting device configured to produce a halogen-like dimming effect using light emitting diodes (LEDs). The lighting device includes a first plurality of white LEDs, a second plurality of white LEDs, and one or more third LEDs. The second plurality of white LEDs are arranged in series with the one or more third LEDs, while the first plurality of white LEDs are arranged in parallel with the second plurality of white LEDs and the one or more third LEDs. Each of the first plurality of white LEDs has a higher correlated color temperature (CCT) than any of the second plurality of white LEDs. Further, the first plurality of higher CCT white LEDs has a lower total forward voltage than the second plurality of lower CCT white LEDs. The one or more third LEDs include at least one amber LED and / or at least one lime LED. A driver generates a dimmable output current based on a dimming factor. A pulse width modulation (PWM) signal generator produces a PWM control signal with a duty cycle corresponding to a current sensing signal. The current sensing signal is generated based on the output current of the driver. When the PWM signal is high, a switch in series with the first plurality of lower forward voltage white LEDs will turn on, diverting all driver output current away from the second plurality of higher forward voltage white LEDs. When the PWM control signal goes low, the switch turns off, and the driver output current will flow through the second plurality of higher forward voltage, lower CCT, white LEDs. Rapidly switching (at a rate faster than 24 Hz) between the two types of white LEDs effectively blends the output light of the white LEDs together, enabling the halogen-like dimming effect, while the amber and / or lime LEDs of the one or more third LEDs provide black body curve correction.

[0039] Turning now to the figures, FIG. l is a schematic of a non-limiting example of a dimmable LED lighting device 100. Generally, the lighting device 100 includes a first plurality of white LEDs 102, a second plurality of white LEDs 106, one or more third LEDs 110, a first switching circuit 118, a bypass circuit 134, a dimmer 142 (such as a line phase-cut dimmer, a 0-10V dimmer, or other type of dimmer), a current sensor 144, and a current sensing resistor 146. The driver 112 and the dimmer 142 are electrically coupled to a source 200, such as an alternating current (AC) source. In some other embodiments, the dimmer 142 is only coupled to the driver 112 in a 0-10V scheme, a (Digital Addressable Lighting Interface) DALI scheme, or other types of control schemes. In the example of FIG. 1, the source 200 is external to the lighting device 100 (such as a wall outlet), but in other examples, the source 200 may be an internal component of the lighting device 100 (such as a battery). The driver 112 is configured to provide an output current 114 (represented by Io in FIG. 1) to power the various LEDs 102, 106, 110. The amplitude of the output current 114 is controlled by the dimmer 142. The dimmer 142 may be controlled through any practical means. In some examples, the dimmer 142 may be a physical switch or dial capable of being manually adjusted by a user. In other examples, the dimmer 142 may be electronically controlled through a digital user interface. The dimmer 142 provides a dimming factor 116 to the driver 112. The dimming factor 116 ranges between 0.0 and 1.0, where 0.0 represents the lighting device 100 turned fully off, and 1.0 represents the lighting device 100 turned fully on.

[0040] As further shown in FIG. 1, the current sensor 144 is configured to detect the current value of the output current 114 flowing through the current sensing resistor 146. The current sensing resistor 146 typically has a low resistance value, such as less than or equal to 50 milliohms. Ideally, the current sensing resistor 146 provides just enough resistance for the current sensor 144 to capture the value of the output current 114 without generating significant voltage drop or power consumption. Based on the output current 114 flowing through the current sensing resistor 146, the current sensor 144 generates a current sense signal 120. As will be explained in more detail below, the current sense signal 120 is used to control the rapid switching of the LEDs 102, 106, 110 to produce the desired halogen-like dimming effect.

[0041] FIG. 1 illustrates three groups of LEDs. The first group of LEDs is the first plurality of white LEDs 102 (also referred to as the first white LEDs 102). Generally, the first plurality of white LEDs 102 are configured to provide a lighting output corresponding to a fully-on, undimmed incandescent halogen lighting fixture. The first plurality of white LEDs 102 are coupled to the current sense resistor 146 and the first switching circuit 118. Further, the first plurality of white LEDs 102 has a lower total forward voltage than the second group of LEDs. Accordingly, when the first switching circuit 118 is closed, current only flows through the lower total forward voltage white LEDs 102, resulting in illumination. In the non-limiting example of FIG. 1, each of the first plurality of white LEDs 102 has a first CCT 104 of 3000K resulting in warm white light when illuminated. Further, in the non-limiting example of FIG. 1, the first plurality of white LEDs 102 are arranged as three parallel strings of six LEDs in series. Accordingly, the non-limiting example of FIG. 1 includes eighteen of the first plurality of white LEDs 102.

[0042] The second group of LEDs is the second plurality of white LEDs 106 (also referred to as the second white LEDs 106). The second plurality of white LEDs 106 has a higher total forward voltage than first plurality of white LEDs 102. The second plurality of white LEDs 106 are coupled to the current sense resistor 146 and the one or more third LEDs 110. Thus, the second plurality of white LEDs 106 and the one or more third LEDs 110 are arranged in parallel with the first plurality of white LEDs 102 and a series controller switch 138. In the non-limiting example of FIG. 1, each of the second plurality of white LEDs 106 has a second CCT 108 of 1400K resulting in even warmer white light than the first plurality of LEDs 102 when illuminated. Regardless of the specific CCT values, the first CCT 104 should be greater than the second CCT 108. Further, in the non-limiting example of FIG. 1, the second plurality of white LEDs 106 are arranged as eight series LEDs.

[0043] The third group of LEDs is the one or more third LEDs 110. As shown in FIG. 1, the one or more third LEDs 110 are coupled between the second plurality of LEDs 106 and ground. The one or more third LEDs 110 may include one or more amber LEDs 150 and one or more lime LEDs 152. In the non-limiting example of FIG. 1, the one or more third LEDs 110 include one amber LED 150 and one lime LED 152. However, other combinations are possible. Further, the total number of the third LEDs 110 may be proportional to the total number of the first and second pluralities of white LEDs 102, 106, respectively. In some examples, the ratio of the second white LEDs 106 to the third LEDs 110 may be three-to-one. The one or more third LEDs 110 are controlled by the bypass circuit 134. The bypass circuit 134 is configured to bypass the one or more third LEDs 110 when black body curve correction is not needed.

[0044] The first plurality of white LEDs 102 is further defined by a first total forward voltage 122. Similarly, the second plurality of white LEDs 106 is defined by a second total forward voltage 124. In the non-limiting example of FIG. 1, the first total forward voltage 122 is the forward voltage across the entire configuration of all eighteen first white LEDs 102, while the second total forward voltage 124 is the forward voltage across all eight second white LEDs 106. However, in the non-limiting example of FIG. 1, the first total forward voltage 122 is less than the second total forward voltage 124 due to the arrangement of the first plurality of white LEDs 102 into three parallel strings. In some examples, additional parallel strings may be added if additional output light is desired without affecting the relative total forward voltage values (i.e., maintaining the first total forward voltage 122 as less than the second total forward voltage 124). Accordingly, when the first switching circuit 118 is closed, all of the output current 114 will flow through the first plurality of white LEDs 102, and the second plurality of white LEDs 106 (and the one or more third LEDs 110) will be inactive. Similarly, when the first switching circuit is open, no current will flow through the first plurality of white LEDs 102, and the second plurality of white LEDs 106 (and, unless bypassed by the bypass circuit 134, the one or more third LEDs 110) will be activated. The total number of LEDs in each group may be chosen to achieve the desired blend of the various types of light at the various dimming factors 116. The current flowing through the first plurality of white LEDs 102 is represented by I30 in FIG. 1, while the current flowing through the second plurality of white LEDs 106 is represented by I14.

[0045] Blending the light generated by the groups of LEDs is controlled by rapidly switching the first switching circuit 118 on and off. As previously noted, when the first switching circuit 118 is closed (on), the first plurality of LEDs 102 are powered on, and the second plurality of LEDs 106 are powered off. Similarly, when the bypass circuit 134 is open (off), the first plurality of LEDs 102 are powered off, and the second plurality of LEDs 106 are powered on. In the non-limiting example of FIG. 1, this switching is controlled by a pulse width modulation (PWM) signal generator 126 and a first switch 138. The PWM signal generator 126 is configured to generate a PWM control signal 128 to control the first switch 138. A duty cycle 130 of the PWM control signal 128 is proportional to the current sense signal 120. Thus, when the current sense signal 120 indicates that the dimming factor 116 is 1.0, the duty cycle 130 is set to 100%, and the first plurality of white LEDs 102 will remain permanently powered on. If the current sense signal 120 indicates that the dimming factor 116 is 0.75, the duty cycle is 75%, and the first plurality of white LEDs 102 will be powered on for 75% of the time, while the second plurality of white LEDs 106 will be powered on for 25% of the time. If the current sense signal 120 indicates that the dimming factor 116 is 0.5, the duty cycle is 50%, and the first plurality of white LEDs 102 and the second plurality of white LEDs 106 will each be powered on for 50% of the time. This inverse relationship is depicted by the pulse waves shown next to the I30 and I14 currents shown in FIG. 1. Further, the switching frequency 132 of the PWM control signal 128 is at least 24 Hz. Accordingly, the output current 114 generated by the driver 112 determines both the intensity of the light produced by the LEDs 102, 106, 110 as well as the amount of time the LEDs are active to create the desired blend of light at the various dimming factors 116. In the non-limiting example of FIG. 1, the first switch 138 is implemented as a transistor, namely a MOSFET. However, any practical type of switching component may be used.

[0046] In the non-limiting example of FIG. 1, the one or more third LEDs 110 are activated or deactivated according to a window comparator 136 and a second switch 154. The window comparator 136 determines if the current sense signal 120 is within a dimming window 140 to control the second switch 154. In some examples, the dimming window may correspond to dimming factors 116 less than 0.1 and greater than 0.9, as black body curve correction is not required at very low or very high dimming factors 116. If the current sense signal 120 is within the dimming window 140, the one or more LEDs 110 will remain active and illuminate when current flows through the second plurality of white LEDs 106. If the current sense signal 120 is outside of the dimming window 140, the one or more LEDs 110 will remain inactive even when current flows through the second plurality of white LEDs 106. In the non-limiting example of FIG. 1, the second switch 154 is implemented as a transistor, namely a MOSFET. However, any practical type of switching component may be used.

[0047] FIG. 2 is a plot of currents of the first plurality of white LEDs 102 and the second plurality of white LEDs 106 along a range of dimming factors 116, while FIG. 3 is a plot of overall CCT produced by the lighting device 100. In FIG. 2, the current values are normalized to a 0 to 1 scale. As previously noted, Iorepresents the output current 114 from the driver 112, d represents the dimming factor 116, Imaxis the maximum output current produced by the driver 112 prior to dimming, I30 represents the current flowing through the first plurality of white LEDs 102, and I14 represents the current flowing through the second plurality of white LEDs 106. Thus, the output current 114 may be represented by equation 1, the current flowing through the first plurality of white LEDs 102 may be represented by equation 2, and the current flowing through the second plurality of white LEDs 106 may be represented by equation 3 :

[0048] / 0dlmax(1)

[0049] Accordingly, the currents flowing through the LEDs 102, 106 follow second degree, parabolic curves as shown in FIG. 2. The / 14current is a parabola with a maximum current of 0.25Imaxat a 50% dimming factor 116. The second-degree behavior of the currents / 14and / 30is the result of dimming combined with a linear transition in current division between first and second white light LEDs 102, 106. Further, it can be observed that the sum of values of each of the plots at a specific dimming factor 116 is the amplitude of the output current 114 produced by the driver 112. For example, at a dimming factor 116 of 0.5 (shown graphically at 50%), lu and I30 are each approximately 0.25, thereby totaling 0.5 of output current 114. Additionally, it can also be observed that each of the plots add up to a linear function, as the second-degree variables cancel out when summed. The total CCT of output light produced by the lighting device 100 as shown in FIG. 3 has a non-linear response due to the non-linear relationship of the LEDs 102, 106 to current.

[0050] FIG. 4 is a plot of a black body curve and four types of LEDs. In particular, FIG. 4 shows a first white LED 102 and a second white LEDs 106 arranged on the black body curve. In this example, the first CCT 104 of the first white LED 102 is 3000K, and the second CCT 108 of the second white LED 106 is 1400K. The plot illustrates that linearly dimming between the two types of white LEDs 102, 106 results in light output off of the black body curve. Thus, amber LEDs 150 and green (lime) LEDs 152 shown in FIG. 4 are used to adjust the chromaticity of the output light to the black body curve.

[0051] FIG. 5 modifies the current plot of FIG. 2 to include the current flowing through the one or more third LEDs 110 for black body curve correction (also referred to as Du,v correction). In particular, the current flowing through the one or more third LEDs 110 is determined and optimized through mathematical analysis. In some examples, this correction current through the one or more third LEDs 110 could be implemented through a microcontroller, a look-up table, and / or similar means. However, as can be observed in FIG. 5, rather than applying the correction current to the one or more third LEDs 110 via a look-up table and a dedicated PWM signal, the correction current may instead be provided by simply scaling down the current through the second plurality of white LEDs 106.

[0052] FIG. 6 illustrates applying an approximated correction current through the one or more third LEDs 110 by scaling down the current through the second plurality of LEDs 106. In the example of FIG. 6, the scaling factor is approximately 30%. Thus, in order to provide current to the one or more third LEDs 110 according to this scaling factor, the lighting device 100 includes approximately one amber or lime LED 150, 152 for every three second white LEDs 106. Accordingly, applying the approximated correction current through the one or more third LEDs 110 corrects the chromaticity of the output white light of the lighting device 100 to produce a halogen-like dimming effect without requiring a microcontroller, a lookup table, and / or a dedicated PWM signal. This configuration is also driver agnostic, and may be incorporated into an existing lighting fixture or device. FIG. 7 illustrates the resulting CCT of output light generated by the lighting device 100 when black body curve correction is implemented with the amber and / or lime LEDs 150, 152. Accordingly, the CCT plot illustrating in FIG. 7 corresponds to the CCT provided by a halogen bulb at various dimming levels. All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and / or ordinary meanings of the defined terms.

[0053] The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.”

[0054] The phrase “and / or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with “and / or” should be construed in the same fashion, i.e., “one or more” of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the “and / or” clause, whether related or unrelated to those elements specifically identified.

[0055] As used herein in the specification and in the claims, “or” should be understood to have the same meaning as “and / or” as defined above. For example, when separating items in a list, “or” or “and / or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of’ or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e. “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of.”

[0056] As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified.

[0057] It should also be understood that, unless clearly indicated to the contrary, in any methods claimed herein that include more than one step or act, the order of the steps or acts of the method is not necessarily limited to the order in which the steps or acts of the method are recited.

[0058] In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of’ and “consisting essentially of’ shall be closed or semi-closed transitional phrases, respectively.

[0059] The above-described examples of the described subject matter can be implemented in any of numerous ways. For example, some aspects may be implemented using hardware, software, or a combination thereof. When any aspect is implemented at least in part in software, the software code can be executed on any suitable processor or collection of processors, whether provided in a single device or computer or distributed among multiple devices / computers.

[0060] Other implementations are within the scope of the following claims and other claims to which the applicant may be entitled.

[0061] While various examples have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and / or structures for performing the function and / or obtaining the results and / or one or more of the advantages described herein, and each of such variations and / or modifications is deemed to be within the scope of the examples described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and / or configurations will depend upon the specific application or applications for which the teachings is / are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific examples described herein. It is, therefore, to be understood that the foregoing examples are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, examples may be practiced otherwise than as specifically described and claimed. Examples of the present disclosure are directed to each individual feature, system, article, material, kit, and / or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and / or methods, if such features, systems, articles, materials, kits, and / or methods are not mutually inconsistent, is included within the scope of the present disclosure.

Claims

CLAIMS1. A lighting device (100), comprising: a first plurality of white light emitting diodes (LEDs) (102), wherein each of the first plurality of white LEDs (102) has a first correlated color temperature (CCT) (104); a second plurality of white LEDs (106), wherein each of the second plurality of white LEDs (106) has a second CCT (108), and wherein the first CCT (104) is greater than the second CCT (108); one or more third LEDs (110) arranged in series with the second plurality of white LEDs (106); a driver (112) configured to provide an output current (114) to the first plurality of white LEDs (102) or the second plurality of white LEDs (106) according to a dimming factor (116); a switching circuit (118) configured to direct the output current (114) to either the first plurality of white LEDs (102) or the second plurality of white LEDs (106) based on a current sensing signal (120); and a bypass circuit (134) configured to activate or bypass the one or more third LEDs (110) according to the output current (114).

2. The lighting device (100) of claim 1, wherein the first CCT (104) is approximately 3000K.

3. The lighting device (100) of claim 1, wherein the second CCT (108) is approximately 1400K.

4. The lighting device (100) of claim 1, wherein the first plurality of white LEDs (102) comprises two or more parallel strings of white LEDs.

5. The lighting device (100) of claim 4, wherein each of the two or more parallel strings comprises an equal number of white LEDs.

6. The lighting device (100) of claim 1, wherein the first plurality of white LEDs(102) are arranged in parallel with the second plurality of white LEDs (106) and the one or more third LEDs (110).

7. The lighting device (100) of claim 1, wherein the one or more third LEDs (110) comprise at least one amber LED (150) and / or at least one lime LED (152).

8. The lighting device (100) of claim 1, wherein a first total forward voltage (122) of the first plurality of white LEDs (102) is less than a second total forward voltage (126) of the second plurality of white LEDs (106).

9. The lighting device (100) of claim 1, wherein, if the dimming factor (120) is 100%, the second plurality of white LEDs (106) and the one or more third LEDs (110) are deactivated.

10. The lighting device (100) of claim 1, wherein the switching circuit (118) comprises a pulse width modulation (PWM) signal generator (126) configured to generate a PWM control signal (128) configured to control the first plurality of white LEDs (102), and wherein the PWM control signal (128) is generated based on the current sensing signal (120).

11. The lighting device (100) of claim 10, wherein a duty cycle (130) of the PWM control signal (128) is proportional to the dimming factor (116).

12. The lighting device (100) of claim 10, wherein a switching frequency (132) of the PWM control signal (128) is at least 24 Hz.

13. The lighting device (100) of claim 1, wherein the bypass circuit comprises a window comparator (136), wherein the bypass circuit (134) activates the one or more third LEDs (110) based on the current sensing signal (120) and a dimming window (140) of the window comparator (136).

14. The lighting device (100) of claim 1, wherein the lighting device (100) comprises three of the second plurality of white LEDs (106) for every one of the one or more third LEDs (110).

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