FIELD OF INVENTION:
[001] The present subject matter described herein, in general, relates to the field of LED drivers, in particularly, relates to a sequential RGB/RGBW (Red, Green, 5 Blue, White) LED power drive with fast voltage transient converter to drive multi colour RGBW LED sequentially to generate wide colour range in high power lighting application with improve efficiency.
BACKGROUND AND PRIOR ART:
[002] In colored lighting domain lighting engineering has one common issue 10 with these Red, Green, Blue and White LEDs having different forward voltage. Generally this is solved by following two methods- First method is by driving each color of LED bank with series current regulator in pulses width modulation (PWM). This method enables reproduction of wide range of colors but reduces power efficiency due to power loss in series regulator. This reflects in highest 15 level of heat generation in the current regulator of lowest voltage color bank. In the second method multiple supply rail with different voltages are used to drive each LED bank which solves the heat issue and improves efficiency. This needs four programmable current regulators either linear type in low power or switch mode regulator in higher power. This increases the complexity of circuit and tends 20 to be an expensive solution. Some existing solution are given below:
[003] Patent US 6510995 B2 discloses “RGB LED based light driver using microprocessor controlled AC distributed power system” and uses the second method. It has 3 AC/DC power converter for three LED loads.
[004] US Patent Application Publication No. US2017196052 (A1) 25 discloses a LED linear constant power driver circuit comprising an AC power supply, a rectifier bridge, a LED light string, a master chip, a voltage adjustment resistance, a regulated capacitor, a compensation capacitor and a current adjustment resistance; an input end of the rectifier bridge is connected with the AC power supply, an output end of the rectifier bridge is connected with 30 the LED light string and the master chip, the peripheral circuit of the master chip
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includes the voltage adjustment resistance, the regulated capacitor, the compensation capacitor and the current adjustment resistance that regulates the output average current of the system.
[005] Chinese patent Publication No. CN205336595 (U) discloses a LED high frequency drive circuit that a reducible LED gives out heat including power 5 supply circuit unit, LED luminescence unit and high frequency pulse generating circuit unit, be provided with current regulator diode D6 between the input of the output of power supply circuit unit and LED luminescence unit, current regulator diode D6 pass through germanium tube D16 and connect high frequency pulse generating circuit unit, high frequency pulse generating circuit unit is connected to 10 germanium tube D16's negative pole.
[006] Chinese Patent Publication No. CN205378276 (U) discloses an exchange and directly drive LED automatic control series parallel circuit among LED. When input interchange transient voltage is higher or lower, the controlled mutual series connection of two sets of LED loads of symmetry or parallelly connected. 15 The utility model discloses the use of establishing ties each other of the unit control circuit that still includes two -stage or more multistage number.
[007] US Patent Application Publication No. US2015061517 (A1) discloses a driving circuit includes a rectifier circuit and a LED driver integrated circuit. The LED driver integrated circuit includes a regulator circuit, a voltage detector, a 20 buck boost LED driver, and a common ground terminal. The buck boost LED driver converts the regulated voltage detected into an output driving voltage according to a remaining voltage at a negative terminal of the LED load to drive the LED load.
[008] US Publication No. 20170034880 discloses an LED driver comprising a 25 first stage, wherein the first stage converts AC power from an AC power source into a DC power source. A second stage receiving the DC power source from the first stage and further comprising: a second stage step-down buck converter with a constant current output that receives power from the DC power source; and a second stage intelligent step-down LED driver chip that runs a step down buck 30 converter that produces the constant current output to the external LED load.
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[009] US Publication No. 20160165680 discloses a solid state lighting apparatus including an array of solid state light emitters arranged on or over the substrate and a plurality of driving components arranged on or over the substrate. The driving components are configured to independently activate and deactivate at least some of the solid state light emitters of the array of solid state light emitters 5 during a portion of an alternating current (AC) cycle. A method of providing a solid state lighting apparatus includes providing a substrate, mounting an array of solid state light emitters on or over the substrate, and providing a plurality of driving components on or over the substrate.
[0010] However, above patents/ publications are related to AC driving of single 10 color LED bank (Series/parallel combinations) and integrating array of LED and drive together. These do not deal with color mixing RGB/RGBWLED driving.
[0011] US Publication No. 20140376227 discloses a luminaire including an input connection that receives AC line voltage, one or more chains of LEDs, and one or more drivers for driving each chain of LEDs, all within a housing, which may be 15 in the form of a canopy. Each driver may receive power that is extracted from AC line voltage connected to the input connection and provide one or more outputs that drive at least one of the chains of LEDs. The driver may be an integrated circuit, such as a DT3001 TB (made by Seoul Semiconductor). Thus, in this invention multiple drivers are used for different LED bank. 20
[0012] US Publication No. 20150091451 discloses a lighting control including a primary and a secondary input power connection for connection to a primary (mains) and a secondary (battery) power supply respectively, control circuitry for controlling delivery of power from the input power connections to one or more light sources, sensing circuitry configured to sense an external impedance 25 coupled, in use, to the primary input power connection and a controller for determining a present operating state of the one or more light sources. The invention uses multiple converter and controllers as per the need.
[0013] US Publication No. 20130221368 discloses LED modules having a control MOSFET, or other transistor, in series with an LED. A MOSFET wafer is bonded 30 to an LED wafer and singulated to form thousands of active 3-terminal LED
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modules with the same footprint as a single LED. Despite the different forward voltages of red, green, and blue LEDs, RGB modules may be connected in parallel and their control voltages staggered at 60 Hz or greater to generate a single perceived color, such as white. However, the invention inherently provides each LED with its own driver. 5
[0014] US Publication No. 20060192728 discloses an LED driver for driving a plurality of light emitting diodes (LEDs), comprising a current controller to control power supply of a predetermined power source unit to make a current flowing in the plurality of LEDs reach a predetermined target current value which sequentially changes corresponding to the respective LEDs; a plurality of 10 divergence switches to flow or interrupt the current with respect to each of the plurality of LEDs; a bypass switch being connected in parallel with respect to the plurality of divergence switches and the plurality of LEDs and to flow or bypass the current supplied to the plurality of LEDs by being open or short-circuited; and a switch controller to sequentially open and close the plurality of divergence 15 switches corresponding to change of the target current value and control the bypass switch to be short-circuited in a range where the current supplied to the LEDs increases, corresponding to the rise of the target current value. Thus, this publication uses three LED banks for Red, Blue and Green LED in same time ratio and changes the current level of each LED to produce different colour. This 20 is intended for LCD and DMD apparatus. Change over time from one LED to another is masked by bypass switch and LCD/DMD. In this US patent, a bypass switch is placed across the load to short circuit converter load to mask the time taken to change the current of the converter. During the current change time of all LEDs are bypassed by shorting the current by bypass switch. At high power level 25 getting converter reliability at frequent short circuit at high output current is very difficult. Due to this the present solution suffers changeover masking issues.
[0015] Hence there is a need to drive multi colour RGBW LED sequentially to mix colour with single power conversion. Further, there is a need of a solution which drives all LEDs with same current but fast voltage changeover capability so 30
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that changeover do not need masking/shunting. The present invention has been conceived in view of the aforementioned circumstances.
OBJECTS OF THE INVENTION:
[0016] The principal objective of the present invention is to provide a sequential RGB/RGBW LED Power Drive with fast voltage transient converter. 5
[0017] Another object of the present invention is to use single power converter with fast voltage transient to adopt voltage difference in LEDs which are driven in time sequence.
[0018] Yet another object of the present invention is to produce a wide range of color. 10
[0019] Still another object of the present invention is to provide very cost effective as well as high efficiency RGBW LED drive which can produce various colors without higher heat loss.
SUMMARY OF THE INVENTION:
[0020] The present subject matter herein relates to a sequential RGB/RGBW LED 15 power drive with fast voltage transient converter. The sequential RGB/RGBW LED Power Drive with fast voltage transient converter has a Power converter with an output stage having fast voltage transient response, LED Banks with RGBW diodes, switch devices (MOSFET) and digital control circuit as sequence generator. The sequential RGB/RGBW LED power drive drives different color of 20 LED banks with a single fast voltage transient current controlled converter in time domain sequence. The present current control converter adapts fast to different voltage LED banks as the load bank is switched. The present current control converter provides very cost effective as well as high efficiency RGBW LED drive which can produce various colors without higher heat loss. The time ratio of 25 each color LED bank produces a wide range of color.
[0021] In order to further understand the characteristics and technical contents of the present subject matter, a description relating thereto will be made with reference to the accompanying drawings. However, the drawings are illustrative only but not used to limit scope of the present subject matter. 30
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BRIEF DESCRIPTION OF THE DRAWINGS
[0022] It is to be noted, however, that the appended drawings illustrate only typical embodiments of the present subject matter and are therefore not to be considered for limiting of its scope, for the invention may admit to other equally effective embodiments. The detailed description is described with reference to the 5 accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system or methods in accordance with embodiments of the present subject matter are now described, by way of example, 10 and with reference to the accompanying figures, in which:
[0023] Figure 1 illustrates the block diagram of the circuit, in accordance with an embodiment of the present subject matter;
[0024] Fig. 2 illustrates diagram of the Fast Voltage Transient Converter, in accordance with an embodiment of the present subject matter; 15
[0025] Fig. 3 shows output waveform of the Fast Voltage Transient converter, in accordance with an embodiment of the present subject matter; and
[0026] Fig. 4 illustrates expanded view of the output waveform of the Fast Voltage Transient converter, in accordance with an embodiment of the present subject matter. 20
[0027] The figures depict embodiments of the present subject matter for the purposes of illustration only. A person skilled in the art will easily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein. 25
DESCRIPTION OF THE PREFERRED EMBODIMENTS:
[0028] The present subject matter relates to a sequential RGB/RGBW LED power drive with fast voltage transient converter. The present fast voltage transient converter has a high frequency power converter and a fast voltage changing filter. The fast voltage transient converter with the fast voltage changing filter has an 30 output stage having fast voltage transient response. Further, the RGB/RGBW
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LED power drive has four LED Banks – RGBW, four switch devices (MOSFET) and a digital control circuit as sequence generator. The LED bank has a plurality of RGB/RGBW LEDs. The high frequency power converter is made with fast voltage transient response to control output current to the set value with change of load voltage. The high frequency power converter can be AC/DC or DC/DC 5 power converter depends on the application. The fast voltage changing filter has sufficient inductance or high value inductance and lower output capacitance or low value capacitance. Further, higher inductance of output filter lowers the high frequency ripple in output and does not allow fast change in current whereas lower capacitor at output allows change of output voltage faster. The fast voltage 10 transient converter with the fast voltage changing filter allows converter to maintain output current while changing or switching the LED bank. Fast response of the converter allows output voltage to readjust to the new LED bank voltage very fast in time domain. The LED bank with RGB or RGBW combination produces wide range of color of light. These LED banks are switched ON one by 15 one by digital computed sequence of the digital control circuit or sequence generator to produce actual color mix needed. Different color bank of LEDs are switched ON for different duration depending on the color ration of that particular color. There is always one or other LED bank is loaded to the converter.
[0029] It should be noted that the description and figures merely illustrate the 20 principles of the present subject matter. It should be appreciated by those skilled in the art that conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present subject matter. It should also be appreciated by those skilled in the art that by devising various assembly that, although not explicitly 25 described or shown herein, embody the principles of the present subject matter and are included within its scope. Furthermore, all examples recited herein are principally intended expressly to be for pedagogical purposes to aid the reader in understanding the principles of the present subject matter and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as 30 being without limitation to such specifically recited examples and conditions. The
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novel features which are believed to be characteristic of the present subject matter, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures.
[0030] These and other advantages of the present subject matter would be 5 described in greater detail with reference to the following figures. It should be noted that the description merely illustrates the principles of the present subject matter. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present subject matter and are included within its scope. 10
[0031] Fig. 1 and 2 illustrate the block diagram of the circuit, in accordance with an embodiment of the present subject matter. The present sequential RGB/RGBW LED power drive 100 comprises a fast voltage transient converter 101. The fast voltage transient converter 101 has a high frequency power converter 101a and a fast voltage changing filter 101b. The high frequency power converter 101a 15 converts DC High Voltage power to Switched DC power which is filtered to a DC drive voltage by fast voltage transient filter 101b to drive a plurality of RGB/RGBW LEDs 102. The plurality of LEDs is Red, Green, Blue, and White LED. In the present subject matter, it is important to have output stage with fast voltage transient current controlled converter which allows output voltage of the 20 converter to adopt to the new LED bank forward voltage in very small time. The Fast Voltage Transient voltage Converter 101 has the fast voltage changing filter 101b which has a low output capacitor 101bb and high value inductance 101ba. Further, the Fast Voltage Transient voltage Converter 101 has a high bandwidth current feedback loop which provides fast change of voltage keeping the current 25 controlled while LED load is switched between Red, Green, Blue and White. The high value inductance 101ba and the low value capacitor 101bb.
[0032] For Inductance Value:
[0033] It is known that value of inductance in converter can be calculated as L = (dv X dt)/di 30
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[0034] To keep current maintained during the LED bank change over dv can be taken as the difference of input and average LED bank voltage
dt is 1/20th of LED sequencing timing 166uS for 300Hz
di < 20% of rated system drive current but for stability di > 5% of system current
[0035] For capacitance Value: 5
[0036] Output capacitor value of the converter can be calculated as C = I dt/dv
[0037] To allow large voltage change in less time following need to be considered
I is rated LED drive current;
dt is 1/20th of LED sequencing timing 166uS for 300Hz;
dV is max voltage difference between the LED banks 10
[0038] The inductance value of the high value inductance 101ba is more than 30uH. On the other hand, value of the low value capacitance 101bb is less than 22uF. In order to implement the present subject matter, the output filter must have high value of inductance as compare to capacitance. Higher inductance of the fast voltage changing filter 101b lowers the high frequency ripple in output voltage 15 and does not allow fast change in current whereas lower capacitor at output allows change of output voltage faster.
[0039] The arrangement of the fast voltage changing filter has fast voltage transient and low current transient. Which is desired in the present subject matter, when the plurality of RGB/RGBW LED 102 switches at the output of the fast 20 voltage transient converter 101 to power different colour of LEDs one by one with same set current by intensity control or current reference by digital control circuit 103. The Digital control circuit 103 and switch bank is continuously switching different bank of color LEDs to the output of the fast voltage transient converter 101 which has difference in LED forward voltage and hence the converter need to 25 adapt to new voltage at every change step as shown in waveform in figure 3.
[0040] The waveform as shown in the figure 3 and 4 explain how output voltage of single converter is changing with the change of LED bank. Yellow trace (CH1) is output voltage of the converter. Other three traces are for switch drive of Red LED (CH3), Green LED (CH4) and Blue LED (CH2). Red LED bank has very 30 low forward voltage with respect to other two LEDs which is visible in above
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waveform as 19.7V is Red LED bank where as Green and Blue is about 27.9V. The fast voltage transient converter 101 used in the present application test changes the voltage from 27.9V to 19.7V in just 280uS. This fast transient allows mixing if LED colors with single output converter with sequential drive technique. 5
[0041] Digital Control circuit 103 has the computation of what time ratio the different LED banks of Red, Green, Blue and White needs to be turned ON to represent the desired color depending on the selected LED type. It calculates and generates the required timing signal to drive four power switches (MOSFET) which switches the LED bank to the output of a constant current source fast 10 settling power converter. The digital control circuit 103 is a micro controller which generates time sequence of Red, Green, Blue and White on 4 of its output pins which drives the Switch of respective LED as Shown in figure 1. It converts the required 24bit RGB colour value to sequence of 4 channel representative of RGB into RGBW LED timing. In the present subject matter, there is use of single 15 current source to operate RGBW LED banks. To use single current source, the digital control circuit loads each LED bank at a time to the fast voltage transient converter in repeated manner.
[0042] As shown in the figure 3 and 4, the fast voltage transient converter 101 has voltage waveform in Yellow trace. It is continually changing with change of LED 20 at load. Other three trace is gate drive of Red, Green and Blue LEDs switch. The Yellow trace is at 19.7V when red LED is activated (High in Pink Trace). It is about 29V when green LED is activated (High in Green Trace) and 27V during Blue LED is activated (High in Blue trace). This is indicative of voltage change of 8Volts in just 280uS. 25
[0043] The figure 3 is expanded in the figure 4. One cycle of RGB changeover is expanded in the right waveform of the figure 4. The Red LED bank voltage has been kept very low compare to green and blue LED for the demonstration of the concept. Any of the LED bank can have different voltage. Output voltage of the fast voltage transient converter is about 28.5V when Green LED drive loads 30 Green LED as the Load. For Blue LED has minor lower voltage of 27.9V which
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is adjusted in no time to be observed but red LED has 19.7V of forward voltage and it is shown in the last right transition that power converter changes the output voltage quickly to adjust to the new LED voltage as Red LED drive loads the new bank of LED to the output.
[0044] The present invention is to keep the current constant and keep changing 5 LED bank in time scale for which power converter needs to change its voltage quickly to energize different colour of LEDs with its different forward voltage. In the present subject matter, the fast voltage transient converter maintains the current at same level and change the duration ratio of different colour LED banks to get the right colour mix output. In present invention colour mixing is achieved 10 by changing the time ratio of RGBW LEDs keeping the current constant at a given intensity.
[0045] Thus, sequential driving of color RGBW LEDs feed with single fast transient constant current converter produces realistic color mix with good power efficiency and low heat loss. Time ratio of RGB/RGBW is varied to produce the 15 right required colour and hence this avoids time required to change inductor current for each change of LED bank.
[0046] Although embodiments for the present subject matter have been described in language specific to structural features, it is to be understood that the present subject matter is not necessarily limited to the specific features described. Rather, 20 the specific features and methods are disclosed as embodiments for the present subject matter. Numerous modifications and adaptations of the system/component of the present invention will be apparent to those skilled in the art, and thus it is intended by the appended claims to cover all such modifications and adaptations which fall within the scope of the present subject matter. 25

We claim:
1. A sequential RGB/RGBW light emitting diode (LED) power drive (100) with fast voltage transient converter (101) for driving multi color RGB/RGBW diodes (102), the sequential RGB/RGBW light emitting diode 5 (LED) power drive (100)comprising:
the fast voltage transient converter (101) provides fast change of voltage keeping current controlled, the fast voltage transient converter (101) comprises:
a high frequency power converter (101a) for converting stable 10 DC to fast changing dynamic DC power to drive the plurality of RGB/RGBW light emitting diodes (LED) (102);
a high bandwidth current control feedback loop (101c) to maintain the current;
a fast voltage changing filter (101b) with an output stage having 15 fast voltage transient response to control current to set value with change of voltage, wherein the fast voltage changing filter (101b) comprises a high value inductance (101ba) and a low value capacitor (101bb), wherein the high value inductance (101ba) lowers high frequency ripple in output which does not allow fast change in current 20 and the low value capacitor (101bb) allows change of output voltage at faster rate; and
a plurality of switch devices and a digital control circuit as sequence generator (103) to continuously switch the plurality of RGB/RGBW LED (102) to the output from the fast voltage changing filter (101) which has 25 different forward voltages.
2. The sequential RGB/RGBW light emitting diode (LED) power drive (100) as claimed in claim 1, wherein the fast voltage transient converter (101) is AC/DC or DC/DC power converter made with fast voltage transient 30 response to control output current to the set value with change of load
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voltage and maintain output current while changing or switching the plurality of RGB/RBGW LED (102).
3. The sequential RGB/RGBW light emitting diode (LED) power drive (100) as claimed in claim 1, wherein value of the high value inductance (101ba) is 5 more than 30uH.
4. The sequential RGB/RGBW light emitting diode (LED) power drive (100) as claimed in claim 1, wherein value of the low value capacitor (101bb) is less than 22uF. 10
5. The sequential RGB/RGBW light emitting diode (LED) power drive (100) as claimed in claim 1, wherein combination of RGB or RGBW diodes of the plurality of RGB/RGBW LED (102) produce wide range of color of light with single power conversion and the plurality of RGB/RGBW LED (102) 15 are switched ON one by one by digital computed sequence of the digital control circuit (103) to produce actual color mix.
6. The sequential RGB/RGBW light emitting diode (LED) power drive (100) as claimed in claim 1, wherein different color bank of LEDs from the 20 plurality of RGB/RGBW LED (102) are switched on for different time duration depending on the color ration of that particular color and always one or other LED bank is loaded to the fast voltage transient converter (101).
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7. The sequential RGB/RGBW light emitting diode (LED) power drive (100) as claimed in claim 1, wherein the switch devices are MOSFETs which sequentially open and close according to logics.
8. The sequential RGB/RGBW light emitting diode (LED) power drive (100) 30 as claimed in claim 1, wherein the digital control circuit (103) and the switch devices continuously switch different bank of color LEDs from the
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plurality of RGB/RGBW LED (102) to the output of the fast voltage transient converter (101) having difference in LED forward voltage and adapting to new voltage at every change step.
9. The sequential RGB/RGBW light emitting diode (LED) power drive (100) as claimed in claim 1, wherein the fast voltage transient converter (101) 5 changes forward LED voltage from 27.9V to 19.7V within 280μS allowing mixing of LED colors with single output converter with sequential drive technique.