Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
  • H05B45/20—Controlling the colour of the light
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
  • H05B45/30—Driver circuits
  • H05B45/32—Pulse-control circuits
  • H05B45/325—Pulse-width modulation [PWM]
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
  • H05B45/30—Driver circuits
  • H05B45/357—Driver circuits specially adapted for retrofit LED light sources
  • H05B45/3574—Emulating the electrical or functional characteristics of incandescent lamps
  • H05B45/3577—Emulating the dimming characteristics, brightness or colour temperature of incandescent lamps

Definitions

• the subject matter disclosed herein relates to color tuning of one or more light-emitting diode arrays (LEDs) that comprise a lamp operating substantially in the visible portion of the electromagnetic spectrum. More specifically, the disclosed subject matter relates to a technique to enable a single color-tuning device (e.g., a dimmer) controls a dim-to-warm color-tuning apparatus in which a color temperature of the LEDs decreases as the LEDs are dimmed in intensity.
• a single color-tuning device e.g., a dimmer
• LEDs Light-emitting diodes
• SPD spectral power density
• the SPD is the relative intensity for various wavelengths within the visible light spectrum.
• CCT correlated color temperature
• BBL black-body line
• BBL black-body locus
• FIG. 1 shows a portion of an International Commission on
• CIE Illumination
• BBL black body line
• FIG. 2A shows a chromaticity diagram with approximate chromaticity coordinates of colors for typical red (R), green (G), and blue (B) LEDs, on the diagram, and including a BBL;
• FIG. 2B shows a revised version of the chromaticity diagram of FIG. 2A, with approximate chromaticity coordinates for
• FIG. 3 shows a color-tuning device of the prior art requiring a separate flux control- device and a separate CCT control-device;
• FIG. 4 shows an exemplary embodiment of a color-tuning ⁇ device using a single control -device, in accordance with various embodiments of the disclosed subject matter
• FIG. 5 shows an example of a graph indicating color temperature as a function of luminous flux, in accordance with various embodiments of the disclosed subject matter
• FIG. 6A shows an exemplary embodiment of a color-tuning circuit, in accordance with various exemplary embodiments of the disclosed subject matter
• FIG. 6B shows an exemplary embodiment of a
• microcontroller that may be used with the color-tuning circuit of FIG. 6A;
• FIG. 7 shows an example of a method to provide a dim-to- warm operation of an LED light source in accordance with various exemplary embodiments of the disclosed subject matter.
• components and/or electronic components are housed on one, two, or more electronics boards may also depend on design constraints and/or a specific application.
• LEDs Semiconductor-based light-emitting devices or optical power-emitting-devices, such as devices that emit ultraviolet (UV) or infrared (IR) optical power, are among the most efficient light sources currently available. These devices may include light emitting diodes, resonant-cavity light emitting diodes, vertical-cavity laser diodes, edge-emitting lasers, or the like (simply referred to herein as LEDs). Due to their compact size and low power requirements, LEDs may be attractive candidates for many different applications. For example, they may be used as light sources (e.g., flash lights and camera flashes) for hand-held battery-powered devices, such as cameras and cellular phones. LEDs may also be used, for example, for automotive lighting, heads-up display (HUD) lighting, horticultural lighting, street lighting, a torch for video, general illumination (e.g., home, shop, office and studio lighting, theater/stage lighting, and
• HUD heads-up display
• horticultural lighting
• a single LED may provide light that is less bright than an
• incandescent light source and, therefore, multi-junction devices or arrays of LEDs (such as monolithic LED arrays, micro LED arrays, etc.) may be used for applications where enhanced brightness is desired or required.
• LEDs such as monolithic LED arrays, micro LED arrays, etc.
• LED-based lamps or related illumination devices
• a temperature of the LED-based lamps or a single lamp
• a relative brightness e.g., luminous flux
• an end- user may desire that the lamps decrease in color temperature as the lamps are dimmed.
• Such environments may include, for example, retail locations as well as hospitality locations such as restaurants and the like.
• another lamp metric is the color- rendering index (CRI) of the lamp.
• CRI is defined by the
• CIE International Commission on Illumination
• Dm Another quantitative lamp metric
• the Dm> is a metric defined in, for example, CIE 1960, to represent the distance of a color point to the BBL It is a positive value if the color point is above the BRL and negative if below. Color points above the BBL appear greenish and those below the BBL appear pinkish.
• the disclosed subject matter provides an apparatus to control a color temperature relative to a brightness level of the lamp. As described herein, the color temperature is related to both CCT and D ; in color-tuning applications.
• the disclosed subject matter is directed to a hybrid-driving scheme for driving various colors of LEDs including, for example, primary color (Red-Green-Blue or RGB) LEDs, or desaturated (pastel) RGB color LEDs, to make light of various color temperatures with a high color-rendering index (CRI) and high efficiency, specifically addressing color mixing using phosphor-converted color LEDs.
• RGB primary color
• PMI color-rendering index
• CCT temperature temperature tuning applications.
• Some of the advanced color LEDs have desaturated color points and can be mixed to achieve white colors with 90+ CRI over a wide CCT range.
• Other LEDs having 80+ CRI implementations, or even 70+ CRI implementations, may also be used with the disclosed subject matter. These possibilities use LED circuits that realize, and increase or maximize, this potential.
• the control circuits described herein are compatible with single-channel constant-current drivers to facilitate market adoption.
• dimming an LED can be achieved by, for example, reducing the forward current transferred to the LED.
• a controller box (described in detail with reference to FIG. 6A, below) may rapidly switch selected ones of the LEDs between“on” and“off’ states to achieve an appropriate level of dimming and color temperature for the selected lamp.
• LED drive circuits are formed using either an analog-driver approach or a pulse-width modulation (PWM)-driver approach.
• an analog driver all colors are driven simultaneously. Each LED is driven independently by proriding a different current for each LED.
• the analog driver results in a color shift and currently there is not a way to shift current three ways. Analog driving often results in certain colors of LEDs being driven into low current mode and other times, into very high current mode. Such a wide dynamic range imposes a challenge on sensing and control hardware.
• each color is switched on, in sequence, at high speed.
• Each color is driven with the same current.
• the mixed color is controlled by changing the duty cycle of each color. That is, one color can be driven for twice as long as another color to add into the mixed color. As human vision is unable to perceive very fast changing colors, the light appears to have one single color.
• the first LED is driven with a current for a predetermined amount of time
• th en the second LED is driven with the same current for a predetermined amount of time
• the third LED is driven with the current for a predetermined amount of time.
• Each of the three predetermined amounts of time may be the same amount of time or different amounts of time.
• the mixed color is therefore controlled by changing the duty cycle of each color. For example, if you have an RGB LED and desire a specific output, red may be driven for a portion of the cycle, green for a different portion of the cycle, and blue is driven for yet another portion of the cycle based on the perception of the human eye. Instead of driving the red LED at a lower current, it is driven at the same current for a shorter time. This example demonstrates the downside of PWM with the LEDs being poorly utilized, therefore leading to an inefficient use of power.
• Another advantage of the disclosed subject matter over the prior art is that the desaturated RGB approach can create tunable light on and off the BBL while maintaining a high CRI.
• Various other prior art systems in comparison, utilize a CCT approach where tunable color-points fall on a straight line between two primary colors of LEDs (e.g., R-G, R-B, or G-B).
• FIG. 1 shows a portion of an International Commission on Illumination (CIE) color chart 100, including a black body line (BBL) 101 (also referred to as a Pianckian locus) that forms a basis for understanding various embodiments of the subject matter disclosed herein.
• the BBL 101 shows the ehrornaticity coordinates for
• blackbody radiators of varying temperatures It is generally agreed that, in most illumination situations, fight sources should have ehrornaticity coordinates that lie on or near the BBL 101.
• ehrornaticity coordinates that lie on or near the BBL 101.
• Various mathematical procedures known in the art are used to determine the “closest” blackbody radiator.
• this common lamp specification parameter is called the correlated color temperature (CCT).
• CCT correlated color temperature
• a useful and complementary way to further describe the ehrornaticity is provided by the Duv value, which is an indication of the degree to which a lamp’s ehrornaticity coordinate lies above the BBL 101 (a positive Duv value) or below the BBL 101 (a negative D uv value).
• the portion of the color chart is shown to include a number of isothermal lines 117. Even though each of these lines is not on the BBL 101, any color point on the isothermal line 117 has a constant CCT.
• a first isothermal line 1G7A has a CCT of 10,000 K
• a second isothermal line 117B has a CCT of 5,000 K
• a third isothermal line 117C has a CCT of 3,000 K
• a fourth isothermal line 117D has a CCT of 2,200 K.
• the CIE color chart 100 also shows a number of ellipses that represent a Macadam Ellipse (MAE) 103, which is centered on the BBL 101 and extends one step 105, three steps 107, five steps 109, or seven steps 111 in distance from the BBL 101.
• the MAE is based on psychometric studies and defines a region on the CIE chromaticity diagram that contains all colors which are indistinguishable, to a typical observer, from a color at the center of the ellipse.
• each of the MAE steps 105 to 111 (one step to seven steps) are seen to a typical observer as being substantially the same color as a color at the center of a respective one of the MAEs 103.
• a series of curves, 115A, 115B, 115C, and 115D represent substantially equal distances from the BBL 101 and are related to D uv values of, for example, +0.006, +0.003, 0, - 0.003 and - 0.006, respectively.
• FIG. 2A shows a chromaticity diagram 200 with approximate chromaticity coordinates of colors for typical coordinate values (as noted on the x-y scale of the chromaticity diagram 200) for a red (K) LED at coordinate 205, a green (G) LED at coordinate 201, and a blue (B) LED at coordinate 203.
• FIG. 2 A shows an example of the chromaticity diagram 200 for defining the wavelength spectrum of a visible light source, in accordance with some embodiments.
• the chromaticity diagram 200 of FIG. 2A is only one way of defining a wavelength spectrum of a visible light source; other suitable definitions are known in the art and can also be used with the various embodiments of the disclosed subject matter described herein.
• a convenient way to specify a portion of the chromaticity diagram 200 is through a collection of equations in the x-y plane, where each equation has a locus of solutions that defines a line on the chromaticity diagram 200.
• the lines may intersect to specify a particular area, as described below in more detail with reference to FIG. 2B.
• the white light source can emit light that corresponds to light from a blackbody source operating at a given color temperature.
• the chromaticity diagram 200 also shows the BBL 101 as described above with reference to FIG. 1.
• Each of the three LED coordinate locations 201, 203, 205 are the CCT coordinates for“fully- saturated” LEDs of the respective colors green, blue, and red.
• FIG 2B shows a revised version of the chromaticity diagram 200 of FIG. 2A.
• the chromaticity diagram 250 of FIG. 2B shows approximate chromaticity coordinates for desaturated (pastel) R, G, and B LEDs in proximity to the BBL 101. Coordinate values (as noted on the x-y scale of the chromaticity diagram 250) are shown for a desaturated red (R) LED at coordinate 255, a desaturated green (G) LED at coordinate 253, and a desaturated blue (B) LED at coordinate 251.
• R desaturated red
• G desaturated green
• B desaturated blue
• the desaturated R, G, and B LEDs may be in a range from about 1800 K to about 2500 K. In other embodiments, the desaturated R, G, and B LEDs may be in a color temperature range of about 2700 K to about 6500 K.
• the color rendering index (CRI) of a light source does not indicate the apparent color of the light source; that information is given by the correlated color temperature (CCT). The CRI is therefore a quantitative measure of the ability of a light source to reveal the colors of various objects faithfully in comparison with an ideal or natural-light source.
• a triangle 257 formed between each of the coordinate values for the desaturated R, G, and B LEDs is also shown.
• the desaturated R, G, and B LEDs are formed (e.g., by a mixture of phosphors and/or a mixture of materials to form the LEDs as is known in the art) to have coordinate values in proximity to the BBL 101. Consequently, the coordinate locations of the respective desaturated R, G, and B LEDs, and as outlined by the triangle 257, has a CRI have approximately 90 or greater.
• a correlated color temperature may he selected in the color-tuning application described herein such that all combinations of CCT selected all result in the lamp having a CRI of 90 or greater.
• Each of the desaturated R, G, and B LEDs may comprise a single LED or an array (or group) of LEDs, with each LED within the array or group having a desaturated color the same as or similar to the other LEDs within the array or group.
• a combination of the one or more desaturated R, G, and B LEDs comprises a lamp.
• FIG. 3 shows a color-tuning device 300 of the prior art requiring a separate flux-control device 301 and a separate CCT- control device 303.
• the flux-control device 301 is coupled to a single channel driver circuit 305 and the CCT-control device is coupled to a combination LED-driving circuit/LED array 320.
• the combination LED-driving circuit/LED array 320 may be a current-driver circuit, a PWM driver circuit, or a hybrid current- driver/PWM- driver circuit.
• Each of the flux-control device 301, the CCT-control device 303, and the single-channel driver circuit 305 is located in a customer facility 310 and all devices must be installed with applicable national and local rules governing high-voltage circuits.
• the combination LED- driving circuit/LED array 320 is generally located remotely from the customer facility 310. Consequently, both the initial purchase price and the installation price may be significant.
• FIG. 4 shows an exemplary embodiment of a color-tuning device 400 using a single control -device 401, in accordance with various embodiments of the disclosed subject matter.
• the single control- device 401 is coupled to a single-channel driver circuit 403, both of which are within a customer installation-area 410.
• the single- channel driver circuit 403 is coupled to a combination hybrid-driving circuit/desaturated LED array 420.
• the combination hybrid-driving circuit/desaturated LED array 420 is generally located remotely from the customer installation-area 410 (but generally still within a customer facility).
• One embodiment of the combination hybrid-driving ⁇ circuit/desaturated LED array 420 is described in detail below with reference to FIGS. 6 A and 6B.
• the color-tuning device 400 requires only a single device to control both luminous flux (and luminous intensity) and color temperature as described in more detail below with reference to FIG. 5.
• the single control-device 401 is a variable-resistance device, such as, for example, a slider-type dimmer (a linearly-operated device) or a rotary-type dimmer.
• the single control- device 401 comprises a voltage divider.
• the single control-device 401 provides a continuous, variable output voltage or a discrete set of output voltages.
• the single control-device 401 may already be in use by the end-user in the customer installation-area 410.
• FIG. 5 shows an example of a graph 500 indicating color temperature 501 as a function of luminous flux 503, in accordance with various embodiments of the disclosed subject matter.
• a curve 505 of the graph 500 indicates that, as the luminous flux 503 increases, a resulting color temperature 501 also increases
• the color temperature of an LED array increases as an end-user of the system (e.g., see FIG. 4) increases the“brightness” (luminous flux) of the array. Conversely, the color temperature of the LED array decreases as the end-user“dims” the LED array. Consequently, various embodiments of the disclosed subject matter describe a dim-to-warm LED circuit.
• the dim-to-warm LED circuit also serves to mimic the dim-to-warm behavior of a standard incandescent light bulb - as an end-user dims the incandescent light bulb, the color temperature of the bulb drops commensurately as well.
• FIG. 6A illustrates an exemplary embodiment of a hybrid driving-circuit 600 for RGB tuning.
• the hybrid driving-circuit 600 includes an LED driver 601 electrically coupled to a voltage regulator 603. Together, the LED driver 601 and voltage regulator 603 produce a stabilized current, lo.
• the hybrid driving-circuit 600 is also shown to include an analog current-division circuit 6 IGA a multiplexer array 620, and an LED multi-colored array 630.
• the LED multi-colored array 630 can include one or any number of a first color of LED arrays 631, one or any number of a second color of LED arrays 633, and one or any number of a third color of LED arrays 635. In various embodiments, more than three colors can be used. Also, the LED arrays 631, 633, 635 can comprise only a single LED in each array.
• the LED arrays 631, 633, 635 can be designed to be tuned using the hybrid driving-circuit 600 as described in detail herein.
• the first color of the LED arrays 631 comprises green LEDs
• the second color of the LED arrays 633 comprises red LEDs
• the third color of the LED arrays 635 comprises blue LEDs.
• any set of colors may be selected for LED arrays 631, 633, 635.
• each of the LED arrays 631, 633, 635 may comprise desaturated green LEDs, desaturated red LEDs, and desaturated blue LEDs, respectively, as described above with reference to FIG. 2B.
• the assigning of colors to particular channels is simply a design choice, and while may other designs are contemplated, the current description uses the color combinations discussed
• the hybrid driving-circuit 600 includes the analog current- division circuit 610A that is configured to divide the incoming current, Io, into two currents I I , and I R , as output on a first branch-line 619L (a left-side current-branch 616L of the analog current- division circuit 610A) and a second branch-line 619R (a right-side current-branch
• the analog current-division circuit 610A may take the form of a driving circuit to provide each of the two branch lines, 619L, 619R with equal currents.
• the analog current- division circuit 610 A may take the form of a driving circuit to provide each of the t wo branch lines, 619L, 619E with unequal currents.
• the analog current -division circuit 610A may further account for any mismatch in forward voltage between different colors of the LEDs while allowing precise control of the drive current in each color.
• the analog current- division circuit 610A may allow for a deliberate, unequal division of current, which cannot be accomplished by simply switching on various combinations of the LED arrays 631, 633, 635 (the switching portion of the circuitry is described in more detail below with reference to the multiplexer array 620).
• other analog current- division circuits may be utilized without departing from the scope of the disclosed subject matter.
• the analog current- division circuit 610 A described herein is provided as one example of a current-divider circuit so the skilled artisan will more fully appreciate the disclosed subject matter.
• the analog current- division circuit 610A may be mounted on, for example, a printed-circuit board (PCB) to operate with the LED driver 601 and the LED multi-colored array 630
• the LED driver 601 may be, for example, a conventional LED driver known in the art. Therefore, the analog current- division circuit 610A can allow- the LED driver 601 to be used for applications utilizing two or more of the LED multi-colored array 630.
• the analog current -division circuit 610A is mounted on, for example, a PCB that is separate from at least one of the LED driver 601 and the LED multi-colored array 630.
• Each current branch of the analog current- di vision circuit 610A may include a sense resistor (e g ⁇ , Rsi and Rs2).
• the analog current -division circuit 610 A includes a first sense-resistor 615L (Rsi) to sense a first voltage, VSENSE_RI, of the left-side current- branch 616L and a second sense-resistor 615R (Rs2) to sense a second voltage, VSENSE__R2, of the right-side current-branch 616R.
• the voltage at VSENSE_RI is produced by the current flowing through the first sense-resistor 615L (Rsi) and the voltage at V SENSE-R 2 is produced by the current flowing through the second sense-resistor 615R (Rsi)
• the analog current -division circuit 610A of FIG. 6 A is also shown to include a computational device 610B.
• the computational device 610B may be used in conjunction with or substituted by a microcontroller, as discussed with reference to FIG. 6B, below-.
• the computational device 610B is configured to compare the first sensed-voltage, VSENSE_RI , and the second sensed-voltage, VSENSE_R2, to determine a set voltage, VSET. If the first sensed-voltage, VSENSEJRI, is lower than the second sensed- voltage, VsENSE__R2, the computational device 610B is configured to increase the set voltage, VSET. If the first sensed-voltage, VSENSEJU, is greater than the second sensed-voltage VSENSEJR2, the computational device 610B is configured to decrease the set voltage, VSET.
• the computational device 610B includes an operational amplifier 612, a capacitor 614 between a location on which the set voltage, VSET, is carried, and ground, and a lower resistor, RLOWER, (serving as a discharge resistor for the capacitor 614) placed in parallel with the capacitor 614.
• an upper resistor, RUPPER is placed in series with both the resistor RLOWER, and the capacitor 614. Benefits of the upper resistor, RUPPER, are discussed below.
• the first sensed-voltage, VSENSE . RU and the second sensed- voltage, Vs ENSE-R2, are fed to the operational amplifier 612.
• the computational device 610B may be configured to compare the first sensed-voltage, VSENSE_RI, to the second sensed-voltage, VSENSE_R2, by subtracting the first sensed-voltage, VSENSE . RU from second sensed- voltage, VSENSE_R2.
• the computational device 610B may be configured to convert the difference of the first sensed-voltage, VSENSE_ . RU and the second sensed-voltage, VSENSE . _R2, into a charging current.
• the charging current is used to charge the capacitor 614, thereby increasing the set voltage, VSET, when the first sensed-voltage,
• VSENSE_ . RU is less than the second sensed-voltage, VSENSE_R2.
• the computational device 610B may be configured to convert the difference of the first sensed-voltage, VSENSE_ . RU and the second sensed-voltage, VSENSE_R2, into the discharging resistor, RLOWER.
• the discharging resistor, RLOWER decreases the set voltage, VSET, when the first sensed-voltage, VSENSE_RI, is greater than the second sensed- voltage , V SENSE ..R 2.
• the computational device 61 OB may decrease the set voltage, VSET, which in turn decreases the first gate-voltage, VGATEI, that supplies power to the left-side current- branch 616L. Consequently, when the operational amplifier 612 is in regulation, the first sensed-voltage, VSENSE_RI, is approximately equal to the second sensed-voltage, VSENSE_R2.
• the ratio of the current of the left-side current-branch 616L to the current of the right-side current-branch 616R is equal to the ratio of the value of the second sense-resistor 615R (Rs2) to the value of the first sense-resistor 615L (Rsi).
• the hybrid driving-circuit 600 divides the current into two equal parts (assuming the current drawn by the auxiliary circuits, such as supply voltage generation, is negligible). It should be noted that, as will be appreciated a person of ordinary skill in the art and as discussed above, the computational device 610B shown in FIG. 6A is just one of many possible embodiments.
• the set voltage, VSET is provided to a voltage-controlled current source.
• the voltage-controlled current source may be implemented with an additional operational amplifier 611.
• the additional operational amplifier 611 then provides a first gate- voltage, VGATEI.
• the first gate-voltage, VGATEI provides an input to a first transistor 613L that provides a driving current-source I I , on the first branch-line 619L.
• the first transistor 613L may be, for example, a conventional metal-oxide semiconductor field-effect transistor (MOSFET).
• MOSFET metal-oxide semiconductor field-effect transistor
• the first transistor 613L may be an n -channel MOSFET.
• first transistor 613L may be any type of switching device known in the art.
• a second transistor 613R provides a driving current-source I R , on the second branch -line 619R.
• the second transistor 613R may also comprise a conventional MOSFET or related device type.
• the second transistor 613R is an n -channel MOSFET.
• the second transistor 613R may onl be switched on when the left-side current -branch 616L is in regulation.
• a second gate voltage, VGATE2 allows current flow through the second transistor 613R.
• the second gate voltage, VGATE2 may be fed to a reference (REF) input of a shunt regulator 617.
• the shunt regulator 617 has an internal reference voltage of 2.5 V.
• the shunt regulator 617 is configured to sink a large current.
• the voltage applied at the REF node of the shunt regulator 617 is less than or equal to about 2.5 V, the shunt regulator 617 may sink a small, quiescent current.
• the of the shunt regulator 617 may comprise a Zener diode.
• the large sinking current pulls the gate voltage of the second transistor 613R down to a level below its threshold voltage, which may switch off the second transistor 613R.
• the shunt regulator 617 may not be able to pull the cathode more than the forward voltage, Vr, of a diode below the REF node.
• the second transistor 613R may have a threshold voltage that is higher than 2.5 V.
• a shunt regulator with a lower internal reference voltage, such as, for example, 1.24 V may be used.
• the upper resistor, RUPPER is placed in series with both the resistor RLOWBR, and the capacitor 614.
• the computational device 610B (or the microcontroller described below with reference to FIG. 6B) reacts to a 0 V to 10 V analog signal and changes proportions of R/G/B colors of the LED arrays 631, 633, 635 according to an algorithm. In order to make the light change color with the input current, the current needs to be sensed and the signal needs to be rerouted to the 0 V -10 V input.
• the VS EN S E _R I signal is fed to microcontroller or other type of computational device.
• RUPPER a trade-off exists in the prior art circuits between the input dynamic range of an internal analog- to- digital converter (ADC) and the power dissipation in the sense resistors, Rsi and Rsa.
• the inclusion of the resistor, RUPPER, as shown in the hybrid driving-circuit 600 of FIG. 6A improves the aforementioned trade-off between the dynamic range and the power dissipation of the sense resistors.
• the resistor, RUPPER is inserted between the source terminal of the MOSFET coupled to VSET and the resistor, RLOWER, in parallel with the capacitor 614.
• a combination of the two resistors, RUPPER and RLOWER forms a resistive divider.
• One original function of this circuit is to make certain that the quantity VSET, being equal to VSENSEJU and VSENSE_R2 in equilibrium, is still fulfilled.
• the hybrid driving- circuit 600 includes the multiplexer array 620 that is configured to electrically couple two of the three LED arrays 631, 633, 635 to the first branch-line 619L and the second branch -line 619R, providing the two current sources II, IR, created by the analog current-division circuit 610 A.
• the multiplexer array 620 includes a number of switching devices, 621, 623, 625, 627.
• the multiplexer array 620 may include more or fewer switches. In a specific exemplary
• the switching devices, 621, 623, 625, 627 comprise
• the multiplexer array 620 is configured to conduct currents I I and IR into two of the colors of the LED multi-colored array 630 substantially concurrently .
• the hybrid driving-circuit 600 for RGB tuning uses the analog current -division circuit 610A to drive two colors of the three LED arrays 631, 633, 635 substantially simultaneously.
• the hybrid driving-circuit 600 then overlays PWM time-slicing with the third (remaining) color of the three LED arrays 631, 633, 635.
• the ratio between the currents I I and IR may be pre-determined. For example, the ratio between the currents may be 1: 1 or slightly different to maximize efficiency. However, any ratio may be used.
• three virtual color-points can be created (R-G, R-B, G-B), using, for example, the desaturated RGB LEDs described herein.
• the triangle formed by the three virtual color points (R-G, R-B, G-B) defines the gamut of the hybrid-driving subject matter disclosed herein.
• one or more primary colors R/G/B can be included for mixing.
• a microcontroller 650 that may be used in conjunction with or in place of the computational device 610B.
• the microcontroller 650 can perform complex signal processing with potentially fewer PCB resources than the analog circuit described above.
• the skilled artisan will recognize that other types of devices may operate the same as or similarly to the microcontroller 650. A few such device are described below.
• the microcontroller 650 receives input signals and can perform the operations of the switching devices 621, 627 of FIG. 6 A (the first and fourth swatches) the operation of Si and S4.
• the microcontroller 650 is configured to monitor the absolute value of the input current by sensing VsENSEjii at a sense-voltage input 651 and a temperature of the board on which, for example, the microcontroller 650 is located. The temperature is sensed with, for example, a negative temperature- coefficient (NTC) resistor (thermistor, not shown) coupled to an NTC input 655 of the microcontroller 650.
• NTC negative temperature- coefficient
• VSENSE_KI at the sense-voltage input 651 and NTC input 655, can be used to compensate for a potential color shift in the LED arrays 631, 633, 635 due to drive current and temperature.
• the 0 V to 10 V input can be used as a control input 653.
• the microcontroller 650 can be mapped to a CCT tuning curve.
• the microcontroller 650 translates incoming instructions (e.g., color temperature as a function of luminous flux, see FIG. 5) to the operation of the multiplexer array 620.
• the microcontroller 650 can provide a first output signal, 1L, at a first output 657, to control switch Si and a second output signal, I R , to control switch S4 at a second output 659.
• the input current is sensed via sense resistor Rsi and is converted into a voltage, VSENSEJU.
• AMPLIFIED is fed to the computational device 61GB (see FIG. 6A) or to the microcontroller 650 ( see FIG. 6B).
• the microcontroller 650 stores a digitized CCT versus current curve.
• the digitized CCT versus current curve may he established in a variety of ways known to a skilled artisan and stored in software (e.g., within the microcontroller 650), firmware (e.g., an EEPROM), or hardware (e.g., a Field Programmable Gate Array (FPGA)).
• firmware e.g., an EEPROM
• FPGA Field Programmable Gate Array
• the instructions can then select a CCT that corresponds to the sensed current level.
• the maximum current can be hard-coded in the microcontroller 650 and correlated with a maximum color temperature (e.g., e.g., 3500 K).
• the computational device 610B and/or the microcontroller 650 can be configured to adjust
• microcontroller 650 can enter the calibration mode if it is power cycled in a special sequence (e.g., a combination of long and short power-up/down cycles). While in this calibration mode, the user (e.g., a calibrating technician at the factory or an advanced end-user) is asked to change the driver-output current between the minimum and maximum levels of the driver output. The microcontroller 650 then stores these two values in, for example, an internal memory (either to the microcontroller 650 or to a board on which the microcontroller 650 is located) as described above.
• the internal memory can take a number of forms including, for example, electrically erasable programmable read-only memory (EEPROM), phase-change memory (PCM), flash memory , or various other types of non-volatile memory devices known in the art
• FIG. 7 an example of a method 700 to provide a dim-to-warm operation of an LED light source in accordance with various exemplary embodiments of the disclosed subject matter is shown.
• the method 700 describes using, for example, the hybrid driving-circuit of FIG. GA for the dim-to-warm operation of the LED multi-colored array 630.
• the exemplary operations shown enable various ones of the LED multi-colored array 630 to be combined to produce a desired color temperature for a given luminous-signal level from the single control-device of FIG. 4.
• the luminous-signal level received is read by the single-channel driver circuit 403 (e.g., which ay comprise the LED driver 601 of FIG. 6A).
• the luminous-signal level may then be used to calibrate, for example, the computational device 610B and/or the microcontroller 650 as described above.
• the method 700 divides an input current, via an analog current-division circuit, into a first current, I I , and a second current, I R .
• the first current is provided to a first of three colors of the LED multi-colored array 630 and the second current to a second of three colors of the LED multi-colored array 630, substantially
• the first current is provided to the second of the three colors of the LED multi-colored array 630 and the second current is provided to a third of the three colors of the LED multi colored array 630, substantially simultaneously, during a second portion of the period via the multiplexer array 620.
• the first current is provided to the first of the three colors of the LED multi-colored array 630 and the second current is provided to the third of the three colors of the LED multi-colored array 630, substantially simultaneously, during a third portion of the period via the multiplexer array.
• the providing of the first current and the second current to different duplets of the LED multi-colored array 630 may occur using pulse-width modulation (PWM) time slicing to provide a drive current to a third of the three colors of the LED multi colored array 630.
• PWM pulse-width modulation
• the PWM may be substantially equal between the combination of the first of the three colors of LEDs, the second of the three colors of LEDs, and the third of three colors of LEDs.
• the PWM may be different depending on the desired drive characteristics of the LEDs.
• many of the components described may comprise one or more modules configured to implement the functions disclosed herein.
• the modules may constitute software modules (e.g., code stored on or otherwise embodied in a machine-readable medium or in a transmission medium), hardware modules, or any suitable combination thereof.
• a “hardware module” is a tangible (e.g., non-transitory) physical component (e.g., a set of one or more microprocessors or other hardware-based devices) capable of performing certain operations and interpreting certain signals.
• the one or more modules may be configured or arranged in a certain physical manner.
• one or more microprocessors or one or more hardware modules thereof may be configured by software (e.g., an application or portion thereof) as a hardware module that operates to perform operations described herein for that module.
• a hardware module may be implemented, for example, mechanically or electronically, or by any suitable combination thereof.
• a hardware module may include dedicated circuitry or login that is permanently configured to perform certain operations
• a hardware module may be or include a special-purpose processor, such as a field-programmable gate array (FPGA) or an application specific integrated circuit (ASIC).
• FPGA field-programmable gate array
• ASIC application specific integrated circuit
• a hardware module may also include programmable logic or circuitry that is temporarily configured by software to perform certain operations, such as interpretation of the various states and
• a hardware module may include software encompassed within a CPU or other programmable processor. It will be appreciated that the decision to implement a hardware module mechanically, electrically, in dedicated and permanently configured circuitry, or in temporarily configured circuitry (e.g., configured by software) may be driven by cost and time considerations.

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• Circuit Arrangement For Electric Light Sources In General (AREA)

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• 2020
  • 2020-06-23 EP EP20739814.0A patent/EP3991521A1/en active Pending
  • 2020-06-23 JP JP2021576925A patent/JP7106023B2/ja active Active
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  • 2020-06-23 CN CN202080060942.2A patent/CN114271028B/zh active Active
  • 2020-06-23 WO PCT/US2020/039137 patent/WO2020263826A1/en active Application Filing
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