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LED display driver solution are introduced and compared

Several solutions are introduced and compared

TLC5941 driver chips

TLC5941 chip is the latest TI Texas instruments) company, has high point correction, grey scale (PWM) control, etc. TLC5941 all internal data register, gray register, register point calibration and error status information through the serial interface to access to the largest serial clock frequency of 30 MHZ, generally within plus or minus 6%, between the current error between the current error generally within plus or minus 4%, per channel maximum output current 80 ma

TLC5941 each channel available PWM mode according to the internal gray register values for level 4096 gray scale control, the register is 12, each channel LED driver circuit from 6 loci correction control register values for level 64, and the maximum of the drive current can be set off chip resistor. Current control provides a level 64 LED point gray level correction ability, level 4096 gray-scale adjustment is to ensure the even under the low grey scale, each point in the lattice has as many as 256 level gray scale, said to all red, green and blue color can be 16 m color color expression ability, both for high quality color large screen display is especially important compared with traditional color large screen display system, concentration to produce PWM gray-scale control, programmable logic chip (or high speed CPU cache management, gray level correction and point data need to deal with the output, reduce the design complexity, and the PWM gray-scale control has nothing to do with data serial removed, can easily get high frame frequency, obtain good dynamic display effect.

In order to ensure the reliable operation of large color screen, TLC5941 provides each LED all the way open circuit (LOD and temperature detection (TSD ability, the built-in open collector output circuit, is used when something goes wrong alarm. Whichever channel has 16 channel error occurs, the built-in open collector output circuit of the output pin is pulled to the low level, by querying the chip’s internal state information, you will know that which way fails, all the TLC5941 built-in open collector output circuit in the system output pin can be together, through the pull-up resistor receives high level, by monitoring the signal, the system can be in operation in the process of self diagnosis. Meanwhile TLC5941 is suitable for the working environment is poor, the display effect is very demanding and high performance requirements on safety, such as highway LED message sign, large outdoor LED TV, etc.

MBI5028 driver chips

MBI5028 Taiwan MBI macroblock) launched a programmable current gain function of LED driver chips. Built-in string and shift register and the output latch, and adopt PrecisionDr technology to get more superior electrical properties. MBl5028 serial clock frequency is 25 MHZ, largest piece between the current error within the plus or minus 6%, generally between the current error generally within plus or minus 3%, maximum output current is 90 ma

MBI5028 built-in current gain control logic unit and a programmable current gain function of the Share – IO technology, do not need to add additional tube feet, only need to the corresponding pin input a specific sequence of signals, it can be adjusted into MBI5028 special function mode – the current model. In this mode, it can be through the system microcontroller, to write different current gain control logic unit current gain data, lock to save these data, and through the built-in digital to analog converter of sharing, to effectively control the current output. Aging due to the change of working environment and the LED screen, LED brightness will be reduced, such as at a fixed forward current, the brightness of the LED screen deviation will be smaller. Through programmable current gain PrecisionDr technology and function, can adjust the current deviation, compensate for the brightness of the LED screen, get a high quality images at the same time. PrecisionDr technology is used and Shared built-in digital to analog converter, under the same precision, by changing the way of digital code to gain relative to the output current, thus improving image quality of the LED screen.

Current technology can provide the LED display screen with current level, 256 to 1200% of the total dynamic range, provide 256 output current rating. Electrical characteristics and chip packaging, MBI5026 compatibility is better, users don’t have to change for the PCB of the same kind of chip design before, can get a Share – IO technology of current gain technology, can greatly reduce the cost of upgrade. MBI5026 is suitable for the work environment conditions are not demanding, but requires high quality LED driver solution on imaging, such as indoor large LED display and other mid-range screen. MBI5028 also applies to the upgrading of old driver chip.

ST2221C driver chips

ST2221C Taiwan SITI point crystal science and technology) company of China able to launch a LED drive chip. The built-in string and shift register unit, the output latch unit and control unit, the output current is relatively good electrical characteristics. ST2221C serial clock frequency is 25 MHZ, largest piece between the current error within the plus or minus 10%, generally between the current error generally within plus or minus 6%, maximum output current is 120 ma ST2221C contains a 16-channel constant current drive unit, can also drive a 16-way LED applicable to drive some low-end screen, such as indoor LED display information screen and so on the low end.

There is a problem

Power consumption and heat problem

Because of its high output current, power consumption and fever of LED display chip is the first factor of blocking driver chip development. Hand-held LED display that may occur in the future on the drive way, the problem would be particularly. With the progress of LED device manufacturing technology level and the decrease of the drive current, the problem will be solved step by step.

Application cost problem

A 16-bit steady-state current mainstream LED display drive chip can only drive a 16-way LED device. A resolution of 1024 x 768 led display must be used more than driving chip to achieve the desired effect, which makes the cost of materials is quite high. If the driver chip itself USES the scanning mode, a mainstream drive chip can drive multiplexed LED device at a time, will make the cost down many application.

The Trade Directory summary

From the terms of the structure of several LED drive chip manufacturers products, is currently the mainstream chip is mainly divided into three grades. The first class is a chip with gray mechanism, this kind of IC with PWM function, can according to the input data to produce gray, are more likely to form deep gray, display high quality images. Second class is to have the output open circuit detection (LOD temperature overheating protection (TSD brightness adjustment function of the chip, the chip with the additional features and more suitable for specific occasions, such as used for the variable information board, to have the function of the detection error LED chip. Third is without any additional features constant current source chip, this chip is only provided for the LED constant current source, ensure the quality of screen display is good.

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Composition and properties of the LED circuit

Below simple parsing with you about the LED circuit composition has its performance:

A, circuit component

When need to use more LED products, if all the leds in series, will need the LED driver output high voltage: if all the leds in parallel, you need the LED driver output larger electric current. All the leds in series or in parallel, not only limits the strict use of LED, and parallel LED load current is bigger, drive cost will increase, the solution is to use the hybrid mode. Average distribution of the number of leds in series, in parallel, so that allocation on an LED series branch voltage is the same, the same series branch current is basically the same on each of the leds, the brightness is consistent, also close by each series branch of current.

Second, the circuit performance analysis

When a series branch have a LED on the poor quality and short circuit, whether driven by voltage type way or constant current drive mode, through the series circuit current will increase, it is easy to damage the leds in series branch. Large current through the damaged after this string of leds, as a result of the through current is bigger, more performance for open circuit. Disconnect after a LED series branch, if the voltage type drive mode, drive the output current will be reduced, without affecting the rest of the all the LED to normal work.

If using constant current LED driver, due to the output current is kept constant drive, allocation will be increased in the rest of the LED current, easy to damage all the leds. Parallel LED solution is as much as possible, so that when disconnect only one LED, distribution in the rest of the LED current is not large, not affect the rest of the LED to normal work.

This series after parallel lines first line of the method is simple, stable, brightness, high reliability, and low consistency requirements for devices, do not need to specially selected device, even if an individual LED single pipe failure, affect the luminous component is lesser also. In the case of larger changes work environment factors, use the connection form of luminous element relatively ideal effect.

Hybrid mode there is another type of connection, that is, LED will be evenly after the grouping in parallel, then each group together. When there is a poor quality and short circuit, LED both driven by voltage type mode and constant current drive mode, all parallel in this branch of the leds will not bright. If using constant current LED driver, due to drive the output current is kept constant, except in parallel on the short circuit of LED a parallel branch, the rest of the leds are working properly. Assumptions of the large number of leds in parallel, drives drive current is bigger, through the short circuit of the LED current will only grow. After the big electric current through the short circuit of the LED, it is easy to become open circuit. Due to parallel LED more, disconnect after a LED, the average distribution of current change is not big, the rest of the leds can still work normally, so in the whole LED lights there is only one LED is not bright.

Luminous element consisting of before and after the series of mixed connection problems, mainly in the field of a single set of parallel LED because of the difference between the device and the conditions of use, single LED chip could lose in a single set of p-n junction characteristics, short circuit. Individual device short-circuit failure LED to lose their jobs have not yet been current IF the LED goes out, “‘” ’cause the whole through from the short circuit devices, full of the total current and a long time to the short circuit current will make the device internal bonding wire or other parts of the burned, open circuit. At this time, not the failure LED to current, normal light, just working current IF bigger than the original. This is the first luminous element appears in the form of a set of the connection of several LED goes out together, after a period of time in addition to the one of the LED not bright, other reasons LED back to normal again.

Three, the choice of drive

Through the above analysis shows that the collocation of drive and load the LED series/parallel way choice is very important, in constant current drive power type LED, not suitable for the parallel load: similarly, voltage regulator series load type LED driver is not suitable for selection.

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High voltage LED advantages compared with the low voltage LED technology

Under the same output power, high voltage LED drive current is much lower than low voltage needed for the LED. With wafer photoelectric high-pressure blu-ray 1 w LED, for example, its pressure drop is as high as 50 v, i.e it drive current can only 20 ma output power of 1 w, and ordinary positive pressure drop to 3 v 1 wled, need 350 ma drive current to the output 1 w power, so the same output power of high pressure LED to work dissipation power is much lower than low voltage LED, which means that the heat dissipation aluminum housing costs can be greatly reduced.

High voltage LED can sharply reduce the AC – DC conversion efficiency losses. 10 w output power, for example, if the forward voltage drop of 50 v, 1 w LED, high output side can take 2 and 4 string configuration, four leds in series of positive pressure drop to 200 v, that is to say from 220 v alternating current (AC) electric bridge rectifier and drop 20 v. But if we use the forward voltage drop to 3 v low voltage LED 1 w, even 10 together positive pressure drop 30 v, however, that is to say need to from 220 vac mains step-down to 30 VDC. As we know, the lower the input and output differential pressure, AC to DC conversion efficiency is higher, can be seen as using high pressure LED, transformer efficiency can be greatly improved, which can greatly reduce the power loss of AC – DC switch, the heat consumption reduce and can further reduce the cost of cooling shells.

So if use high pressure to develop LED general lighting products, LED the overall power consumption can be greatly reduced, so as to greatly reduce the heat dissipation shell design requirements, such as we can to be thinner and lighter aluminum shell can meet the demand of LED lamps and lanterns, heat dissipation, due to the heat dissipation aluminum shell cost is one of the major cost components of LED lighting lamps and lanterns, aluminum shell effectively reduce cost also means that the overall LED lighting lamps and lanterns is effectively reduce the cost. Thus, LED high-pressure can bring costs and effectively reduce the weight of the LED lighting lamps and lanterns, but the more important is lowered to the cooling system design requirements, thus effectively cleared the LED lighting lamps and lanterns enters the indoor lighting market the biggest technical barrier. As a result, the high voltage LED general lighting market will dominate the future of the LED.

(this paper turn from suppilers)

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LED backlighting lighting/driver IC is introduced

A, model: BL8532
Work style: PFM; The input voltage: 0.8-10 / V; Output voltage: constant current feedback voltage 200-500 mv; Static power: 15 ua; Working frequency: 150 KHZ; The effective rate: 87%; Switch tube: built-in; Current: 500 ma;
Encapsulation: SOT – 89-5.
Summary:
BL8532 is designed for LED application of PFM control mode of switch mode DC/DC booster constant current chips, constant through the external resistors can make output current value at zero ma “500 ma. BL8532 can give one or more parallel or more and two series of LED constant current power supply. Due to the internal integration of the pressure limiting protection module, make the chip load or not in the short load under the condition of not burned chips and peripheral circuit. BL8532 can also through the external resistors to adjust output of 2.5″ 6.0 stable voltage is adjustable. BL8532 adopted high-performance reference voltage circuit structure, and modification technology, introduced in production, to ensure the output voltage of the high precision of output and low temperature drift. Provide BL8532 SOT – 89-5 forms of encapsulation.
Features:
Voltage (0.8 V low startup Iout = 1 ma), 0 ~ 500 ma output current range adjustable (resistance by regulating in), or by the peripheral resistance regulation 2.5 V “constant output voltage 6.0 V. Output current accuracy + / – 10%, low output current temperature drift: + 100 PPM / ℃ only inductance, capacitance, schottky diode, adjust, resistance a few external components, such as efficiency is as high as 80%
Purpose:
Provides energy for high power white LED lamp, constant current source, constant voltage source, used for single or double battery power supply power supply part of the equipment.
2, model: PT1301
Work style: PWM; The input voltage: 0.8-6 / V; Output voltage: 3.3-12 / V; Static power: 14 ua; Working frequency: 500 KHZ; The effective rate: 90%; Switch tube: the inner/outer; : current of 100 ma / 700 ma; Encapsulation: SOT – 89-5; SOT – 23-6.
1: fully compatible RT9266; One day/two alkaline batteries to charge their mobile phone battery;
2: the Vin: 0.8 “6.0 v Vout: 3.3″ 12 v Iout: built-in MOS 100 ma, the largest external MOS expansion flow; The static current ua;
3: using PWM control loop, starting voltage, 0.8 V internal contain 2 a power switch, the lithium electricity power supply when the maximum output current is 700 ma,
4: can an external MOSFET expansion flow, switching frequency, 500 KHZ, the output voltage regulated by two external resistors, ua of static electricity;
5: built-in MOS: 1.5 to 1.5, the output current up to 100 ma.
6: external MOS: 1.5 V voltage step-up 3.3 V output current 250 ma, the 5 V to 12 V output current up to 300 ma.
7: two dry batteries power supply, the output LED 1 w, 3 w/maximum current of 700 ma.
8: encapsulation: SOT – 89-5; SOT – 23-6;
Three, model: PT4101
Work style: PWM; The input voltage: 2.5-6 / V; Output voltage: 40 v;
Working frequency: 1.2 MHZ; Effective rate: 88% loading: SOT – 23-5
PT4101 is a single-section lithium battery powered by up to six series LED step-up converter, when 5 v input, can drive 8 “, 10 leds. PT4101 contains power MOS tube, using fixed frequency mode to regulate the LED current, current and current through an external monitoring resistance to measure this current. Its low feedback voltage of 104 mv can reduce power consumption and improve efficiency. OV foot monitoring the output voltage and the output state due to open the way into the overpressure shutoff converter; contains under-voltage lockout, current limit and overheating protection function, to avoid the output overload when causing damage to the device.
Application: the LED flashlight, LCD backlight, OLED booster.
4, model: PT4102
Work style: PWM; The input voltage: 2.5-6 / V; Output voltage: 40 v;
Working frequency: 1.2 MHZ; Effective rate: 87% loading: SOT – 23-5; Sc70-6 packaging addresses – 6;
PT4102 by single section is a lithium battery (constant current) to drive up to eight series LED step-up converter. PT4102 mode to regulate the LED current with fixed frequency current, and by an external current monitoring resistance to measure this current. Its low feedback voltage of 95 mv can reducing power consumption and efficiency; With current restrictions in order to avoid causing damage to the device when output overload.
Application: the LED flashlight, LCD backlight, OLED booster.
Five, model: PT4105
Work style: PWM; The input voltage: 2.5 to 18 / V; Output voltage: 18 v; Switch tube: built-in;
Working frequency: 500 KHZ; Effective rate: 85% loading: SOP – 8
Use single PT4105 realize 1 w high power LED driver solution, effective operating voltage range of 2.5 ~ 18 v, when the input voltage of 5 ~ 12 v, the conversion efficiency over 90%, when the input voltage is 12 ~ 18 v, the conversion efficiency can be above 85%. Use single PT4105 realize 3 w high power LED driver solution, valid for 6 ~ 18 v working voltage range, the conversion efficiency can be above 85%.
Designed for high power LED lighting driver application of fixed frequency mode step-down voltage integrated circuit, the input voltage up to 18 v, built-in power MOS tube, the output current up to 1 a, can be in a very wide range of input voltage driven single star 1 w (current is 350 ma) or 3 w leds (current is 700 ma), or a variety of high-power LED series/parallel combination. PT4105 internal adopts PWM control, the feedback voltage is 200 mv, only has a high conversion efficiency, containing under-voltage lockout, overheating protection, current limiting protection, and other functions, application design, convenient and simple peripheral circuit, the section is more batteries flashlights, car auxiliary lighting, household decoration lighting, choice of miner’s lamp and other applications. PT4105 SOIC8 package.

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LED lighting driver program in favor of the original number of IC manufacturers and feedback

Is called the fourth generation LED lighting source or green light source, energy saving, environmental protection, long life, small size and other characteristics, can be widely used in all kinds of instructions, display, adornment, back light, general lighting and urban night scene, etc. As used in lighting, LED backlight, display, and many other outstanding performance of the market, in succession to develop the field of LED, number of IC manufacturers engaged in the development of LED driver solution. Ensemble, demonstrated different IC manufacturers according to their own situation to choose their own target market. In common, however, still exists, in the face of the volume, dimming control, cost, the challenges such as conversion efficiency, its coping strategies worth discussing.
The original boundary feedback way become a common choice
LED drive main function is to provide stable and accurate working LED lamp current. LED drive scheme of traditional secondary feedback is used to achieve accurate output current control, through the secondary side of current sampling resistance measurements of LED current, and provide feedback by means of photoelectric coupler. Secondary feedback control can lead to drive the increase in cost, size and conversion efficiency is reduced. Such a case, the original boundary feedback way become a common choice of many LED driver solution provider.
The original feedback way of AC/DC control technology is developed in recent 10 years, the AC/DC control technology, and vice side of the traditional feedback decoupling and 431 compared to the structure of the light, its biggest advantage is to save the two chips and work with a group of components, thus saving space on the system board, reduces the cost and improve the reliability of the system.
New (BCD) of semiconductor LED drive chip AP3766, AP1681 is controlled by its unique original edge (PSR) patented technology, without secondary side feedback circuit, which can realize accurate secondary side LED drive current control. Its built-in temperature compensation, transformer compensation and line voltage compensation technology ensures the drives at all temperature, wide voltage and output current precision under the condition of mass production.
Fairchild semiconductor (Shanghai) co., LTD., also said, for small power LED lighting in the AC input side, using the original edge control architecture of the LED drive circuit has a cost and performance advantages. Such as fairchild semiconductor FSEZ1216 FSEZ1307 and FSEZ1317, they adopted the PSR to save light coupling and other feedback circuit, so as to well balance the cost and performance.
Nanjing micro unita from home are also introduced a similar product, nanjing micro unita LED drive chip ME8165/8108 are adopted the original boundary feedback technology, need not light coupling, greatly reduce product volume, and reduce the cost. Nanjing micro unita is one of the IC company backbone of China huada group, is a dedicated analog integrated circuit chips in product research, development and sales of high-tech enterprises. Products applied to information home appliances, wireless communications, digital communications and network technology and other fields. Nanjing micro unita display occupy larger market share at home, it was revealed that the total number of LED drive shipments last year, more than 700 million.
Display driver achieve precise dimming control
Although the world is not perfect LED drive power supply standard, however industry the rapid development of LED drive power supply requirements continue to increase.
In the LED display application market, accurate control of LED brightness is the main appeal. Zhang Hongyu is introduced, in order to achieve display requirements, needs to make sure the chip used in different temperature conditions and bad environments, chip level and a between, between piece and piece, drive current good consistency between batch and batch.
Nanjing the au driving IC ME2604 applications in full-color LED display performance.
Micro nanjing union launched a display driver IC ME2604 oriented market, it is a low pressure differential, high precision 16 bit constant-current driver chips, which adopted the high precision constant current drive circuit and temperature compensate circuit, current by the power supply voltage (VDD), the change of environmental temperature was controlled at 1%. ME2604 resistance can choose different resistance of Rext ME2604 adjustments to the current size of each output port. Can also on the OE end adopts PWM modulation, the minimum pulse width can reach 50 ns. Accordingly, can precisely control the LED’s luminous intensity.
Backlight driving the market competition is intense, the LED TV
LED backlight driver market is mainly composed of the LED TV, LED monitors, laptops and portable markets such as GPS, DPF, PDVD, its screen size from big to small, the proportion of LED backlight since the childhood, laptop and portable products basically 100% using LED backlit, nearly two years in the LCD monitor and LCD TV and LED backlight permeability is rising rapidly. For nearly two years rise LED TV backlight and LED monitor driver program, schools of thought contend on the market.
Fairchild semiconductor is one of the TV power supply scheme of the main suppliers, LED backlight driver domain is also our key markets. LCD TV backlighting applications is rapidly development and changes, including the number of LED lamp series, current voltage parameters, topology structure and AC – DC part matching, and so on. O2Micro and MPS, he argues, although two semiconductor companies in the LCD TV has the advantages of traditional CCFL backlight on the LED backlight market, will be after a period of market validation can be.
New semiconductor (BCD) with its customers in mainland China and Taiwan market advantage and leading products, has been top TV machine factory in mainland China take the lead in mass production of LED TV backlight driving scheme. O2Micro, MPS, BCD, Supertex, Richtek, etc is one of the leading enterprises in a company.
Mobile phone and PC, portable audio, printer in the color liquid crystal display equipment and so on demand more and more high. ROHM launched for color liquid crystal display of LCD backlight for many kinds of LED driver. LED lights for several aspects according to the size of the display screen can be installed 1 ~ 96 lamp; Dimming function according to the function with low power consumption, to meet the requirements of miniaturization “built-in type, reducing load software automatic RGB dimming type, province space Flash built-in type, such as LED drive, and available only for the individual use of decoration or Flash LED driver.
ChengYang semiconductor MCU manufacturers have also recently launched the small and medium size display LED backlight driver IC integration scheme. Under 10 inch is the main target market, the company is now the new generation of WLED backlight drive series, high drive WLED ability, combined with high integration, small volume, simple application circuit, dc conversion path higher advantages, energy conservation, environmental protection, and have competitive price, in NB, in-car GPS, PDVD, digital photo frame and so on market application widely.
– — – — – — – — – — – — – Indoor Light Fixtures

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LED driver power supply must be need to aluminum electrolytic capacitor?

LED driver power supply’s low a important reason is that driver power supply needed for the life of the aluminum electrolytic capacitor is insufficient, the main reason is that working long hours when the LED lamps and lanterns of internal environmental temperature is very high, lead to aluminum electrolytic capacitor electrolyte was quickly dries, life shortens greatly, general can only work about 5000 hours. And the life of the LED light source is 50000 hours, so the working life of the aluminum electrolytic capacitor as the life of the LED drive power supply short ribs.

Now some suppliers in order to solve this problem, invention of aluminum electrolytic capacitor has the LED drive power supply scheme. But not all of the LED drive power supply suppliers are in favor of this practice. Chen Rong pointed out: “in the production of LED lighting driver power supply don’t have a no electrolytic capacitor drive scheme is adopted, because without it, a lot of pass the test standards, such as EMI testing and flicker-free testing.”

And USES the LED drive power supply scheme of aluminum electrolytic capacitors are usually easily the tests above, if replaced with thin film capacitor and ceramic electric or tantalum capacitance, how about? Thin-film capacitor to achieve the same capacity (general is 100-220 uf), the volume will be very big, and the cost is too high, ceramic capacitor average capacity is too small, such as multiple as ceramic capacitor to realize such a large capacity, the plate area and the cost is too big, tantalum capacitor will have so big capacity, it is too expensive, but the pressure is too low, can not meet the requirements, so for any other type of capacitor, basically not volume is too big, or too expensive, such as for these disadvantages into smaller capacitor capacity, eliminate the ripple effect is not so good, many export products strictly required for certification testing index can’t through, so the high quality LED driver power is still widely used aluminum electrolytic capacitors.

Many vendors claim no electrolytic capacitor of the LED drive power supply scheme, is likely to just get rid of the AC input side aluminum electrolytic capacitor, constant current output to the aluminum electrolytic capacitor should be difficult to remove or replace.

In LED driver power supply architecture Chen Rong said that Japan and the United States will be in a isolation type scheme for the mainstream, because they only 110 v input voltage of the power grid. Which China and Europe will be to isolate type scheme for the mainstream, because their power input voltage up to 220 v, isolation scheme of safety guaranteed, although costs may be high.

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The characteristics of the LED driver IC needs to have

Used to drive white LED LED driver IC accounted for about 50% of the total LED driver market, white LED to many commonly used batteries type handheld portable small display with backlight lighting products. However, this kind of lighting application are mature, in the next five years there will be no high compound annual growth rate. For LED lighting application, compound annual growth rate is far higher than hand-held backlighting lighting products of three of the biggest market is in turn: large flat-panel display high-definition TV, car headlights lighting and general lighting.

As consumers are demanding hd TV has a larger flat panels and higher resolution, the demand for televisions has rapidly the LED from plasma high-definition televisions to high-definition televisions. According to DisplaySearch, plasma HDTV sales peak will appear in 2008, the sales revenue of $24 billion; The LCD high-definition television market will reach $2008 in 75 billion, rose to $93 billion by 2010. Obviously, the LED TV market has begun to “prosperity”.

From the motion blur to color reproduction, LCD high-definition TVS have various shortcomings at present. Current generation hd LCD TV do not have access to true black, and all the colors of the dynamic range is small. Ordinary high-definition televisions with CCFL backlight lighting tube, with only 450 to 650 CD/m2 of contrast. These hd TV’s main problem is that the CCFL backlight lighting cannot be completely shut off local move light or not.

Instead, adopts high brightness LED backlight, LED array (in terms of 46 inches display screen, LED) can contain up to 1600 can be backlit “groups” that move light or shut off locally, so as to realize higher than CCFL design almost an order of magnitude of the contrast (> 4000 CD/m2). In addition, by adjusting the brightness of the backlight LED group, can reproduce more in the middle of the color, so as to make the image more vivid. Another advantage is that can learn from localized completely shut off the LED, so as to reduce the motion blur problem. Through between the frame completely shut off the LED, almost completely eliminate the fuzzy problems caused by the fast moving objects. In dealing with this kind of CCFL backlighting LCD TV is facing rapid motion blur problem, the LED is very important for the response speed is very fast.

The designer’s dilemma

Cold cathode fluorescent lamp (CCFL) is often used to provide large flat-panel display backlighting, but their chromatographic co., LTD., and the colour is not bright enough. RGB LED actually expands the range of visible light. In addition, in the proceedings of the national television system committee (NTSC) definition of the colors, CCFL can shows that about 80% of the NTSC chromatography of RGB can show up to 110%, thereby more accurately show the image on the screen of the primitive style. Using three monochromatic light source, such as red, green and blue (RGB) laser, widest possible chromatography can be obtained.

White LED backlighting, on the other hand, is very suitable for hand-held and mobile display, because white LED shape size is small, easy to drive, sensitive to mechanical stress less, with CCFL is two times longer life expectancy. White LED CCFL in chromatographic aspects, however, there are also shortcomings, because the white LED is equal to the broadband light source. White LED is blue light diode cover phosphor powder form, it transform part of the blu-ray into yellow, combination form of spectrum is seen as the white light.

Compared with monochromatic light source, the RGB leds at a lower cost to provide close to the narrow band of chromatography. RGB LED not only improved the chromatogram, but also improve the efficiency, because the RGB LED only according to the need of red, green and blue emission light energy. Relatively, broadband light source (e.g., white LED, CCFL) issued more don’t need color light, reduce the purity of chromatographic, lost efficiency. Since different colors of RGB LED can drive alone, so RGB LED white light point or color temperature can be corrected, and CCFL and white LED white light points are fixed.

LED dimmer to consider

Traditionally, LED light is use DC PWM signal or filtering signal to adjust the forward current through the leds. Reduce the LED current density adjustable LED light output. Forward current change, however, can lead to LED color change, because the LED color change from current. Many applications such as LCD high-definition televisions and cars backlight does not allow the LED luminous color have any deviation. Due to the different light conditions change and subtle change of light intensity in the human eye can sense, so in these applications need wide dimming range. Using PWM signal to control the LED light is strong, can not change the light color to achieve the LED dimmer.

“True Color PWMTM dimming” through the PWM signal to adjust the LED brightness. It is essentially PWM frequency with the full current on and off the LED. Eye of the limit of 60 frames per second. By improving the PWM frequency (for example, increased to 80 hz to 100 hz), the human eye is feeling continuous pulse light source is connected. In addition, through modulation duty cycle (the length of the “on time”), can control the LED light intensity. Using this approach, LED luminous color remains the same, because the LED current value or zero, or a constant value. Lot of high-definition television designers require up to 3000:1 dimmer than, wide range of light change to adapt to the environment.

conclusion

Obviously, high-definition television sets used in the large LCD flat screen backlight, LED has become the mainstream choice. System designers, however, still need to meet their specific performance requirements of the LED driver IC design. LED driver IC, therefore, must be able to meet the input voltage range and output voltage and current requirements needed for the transformation of the topology, for many different types of LED configuration provides sufficient current and voltage. So, the LED driver IC needs to have the following characteristics, to meet the needs of the designer:

(1) wide input voltage range;

(2) wide output voltage range;

(3) high efficiency transformation;

(4) to strictly regulate the LED current matching;

(5) with a low noise, a constant frequency work;

(6) independent of the current and the dimming control;

(7) wide dimming ratio;

(8) with minimal external components of the plate area small compact solution.

This article from the Trade Directory

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LED drive active thermal management is introduced

LED light source for the lighting industry, the trend of The Times, but overall still did not meet the market requirements, the luminous efficiency and heat dissipation defect is first solved the difficult topic, at present, the industry has developed using active thermal management of LED drive, back into the fold by the built-in heat function, in order to improve the LED in the development of use fixed number of year and heat loss of the author.

In 2007, the U.S. doe’s energy information administration (EIA), published a report, the report notes that the United States (lighting equipment in commercial and residential) a total of about 526 billion kilowatt hours of electricity consumption. If refer to the EIA report of 2008, but found an American nuclear power plants capable of producing 12.4 billion kilowatt hours of electricity. Therefore, through a simple calculation shows that the light in the use of the lighting equipment shall be resulted in 42 of the nuclear power plant electricity. As the population grew, lighting industry must be looking for a new type of lighting light source, in order to improve lighting efficiency and reduce energy consumption.

In the lighting industry, light emitting diode (LED) has long been high hopes to replace traditional incandescent lamp, fluorescent lamp and all kinds of gas discharge light source lighting device, main reason LED to reduce power consumption, and make the soil from harmful chemicals that harm. But even LED the luminous efficiency has gone way beyond the efficient light source such as xenon lamp (HID), but in the internal circuit of brightness and the overall performance is not ideal.

Limited LED the luminous efficiency of the light produced, which had nothing to do with using of materials. Internal LED light-emitting radiation way often in a way, so most of the light will be absorbed and produce heat. Is given priority to with phosphor white LED, because history trafigura displacement effect (Stokes Shift) caused by the heat generated by the LED luminous efficiency is lower. But there are several innovative solutions can improve radiation recombination rate and photon absorption problems, in order to increase the brightness of the leds and luminous efficiency.

Implants in photonic crystals increase brightness

Luminus Devices were the first to put forward a solution, by implantation of photonic crystal, in order to limit (Trapped) waveguide photons in the substrate. Photonic crystal is a naturally occurring substance, in the opal in this type of material you can see the existence of the photonic crystal, the tight structure characteristics, can provide the path of the light radiation, can produce a higher density of the light field intensity, with the characteristics and other characteristics such as such as quantum Wells, optical resonant cavity, can make the LED brightness increased beyond imagination. Need for the application of high brightness, such as plate, liquid crystal display (LCD) projector back lighting and other special applications, these special components are already quite popular, hope that we can application in general lighting equipment in the future.

Each lighting equipment, the service life of the light source the problem often encountered the situation is similar to tungsten filament incandescent bulbs burn out suddenly, or because of the long time use in light material failure due to aging gradually so that the dark, also LED by component junction temperature aging phenomenon. All lighting equipment under the condition of providing stable brightness, after must use fixed number of year, the brightness will gradually less than effective luminance contrast. In different lighting application device, is the service life of the time limit. When using, for example, in the street light attenuation to the brightness of the device is 50%, which represents the use fixed number of year, but the doctor used in endoscopic light source brightness devices may yet attenuation so much.

Through thermal management/brightness LED driver IC management loss

LED the service life of the end on behalf of the illumination brightness is lower than below the available level, and the service life of the LED of the correlation length and the temperature is very high (figure 1). If the curve to 1 as the design reference, wants to design a general-purpose lighting equipment, and the service life of at least 50000 hours after the can has 50% of the original brightness, the junction temperature must be controlled under 100 ℃. Under the premise of without using active cooling, will is a very difficult task. In addition, because the LED can’t use radiation heat problem, this will add to the heat dissipation problems more. Traditional incandescent bulbs can spread out a lot of infra-red heat through radiation, while the leds must consider how to solve the problem of heat dissipation. In addition, in use process, if the instantaneous surface temperature more than manufacturers limited by temperature range and for the life of the light emitting component would be caused by the severe permanent damage.

Figure 1. The temperature of the LED lighting effect

If the LED shall be demoted to handle severe junction temperature, when the lighting system in the design and core component, you must think seriously about two important matters, respectively, thermal management and understanding of the LED driver. Not only in general lighting applications to this two factors must be considered, in other applications also need to be considered. The easiest solution is to use passive thermal management mode, through the heat sink with enough air flow can take away the waste heat. Nuventix developed a kind of active cooling device, this device doesn’t use any of the fan components, but the air flow generated by high speed air ejector, the operational principle of the list is like a car knight one hand holding the back of the truck and by truck to fast and fast, Nuventix cooler is designed by using the similar principle, to provide effective cooling way. This technique has been used in the MR16, PAR20, PAR25 standard lighting equipment.
Solution, another important issue is to use the LED drive mode of active thermal management. Traditionally, the LED driver with constant current source, mainly used to monitor and control into a flow of electricity or more groups of leds. Generally speaking, this is enough to drive the LED, and can keep the same brightness in the process of changing the input voltage size. But with brightness and architecture improvement, LED has been able to provide higher the brightness of the light source, and gradually evolved into heat energy control demand of complete light engine core components.

Use to prevent damage to components or shorten the life, must carry out thermal management, and has a variety of ways to solve this problem. Figure 2 for two different inflexion curve, can be in the temperature rise limit the LED current flow. When junction temperature keeping them in the default temperature range, is via the main control circuit as the current regulation; But when junction temperature than the default scope, will use another set of control circuit limits the current size. Which the inflexion point of junction temperature and driving current attenuation rate, can be in accordance with the different applications and LED manufacturers suggest change.

Figure 2 instances of heat energy back into the fold curve

National semiconductor (NS) launched by the LED drive LM3424, has a built-in heat energy back into the fold function, designer can by adjusting curve (slope) select the desired set point and the system gain value. In the LED general lighting and other special application device (such as emergency notice board), more can grasp the LED because of use fixed number of year or the phenomenon of high temperature damage.

Thermal management improve reliability greatly prolongs the service life of LED

Although the development of LED technology, it has also spawned many new problems. As the LED luminous intensity and efficiency continue to improve, more lighting applications will gradually shift from the traditional light source to a new type of LED light source, and generate more new applications. When introducing a new cooling solution and drive technology, thermal management will become more easy, and can prolong the service life of the LED, LED has the potential need not replace, the incandescent bulbs used in the current difficult to achieve.

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Of PI flicker-free dimmable LED driver IC solution

High brightness LED, low consumption, miniaturization, long service life, etc to promote the rapid development of technology, but the LED lighting technology cost is still high, the radiator is too large, low luminance and dimmer and other challenges. In the design process, the engineer adjust LED conventional tend to meet start slowly, blinking, uneven illumination, etc., so how to solve the problem of the LED flashing as engineers the top priority. If you can provide high precision constant current control (can analyze variable phase Angle of thyristor controller output, to a one-way flow of constant current LED adjustment), enter the EMI filter inductance and capacitance is very small, so effectively flicker-free dimmer can be possible? Recently, Power Integrations (PI) company LinkSwitch – PH series LED driver IC to solve this problem well, the primary side of the product control technology also get rid of the isolated flyback type optical coupling is commonly used in Power supply and auxiliary circuit control circuit (i.e., secondary side), the PFC controller at the same time also save a high capacity electrolytic capacitor, the leds flicker free dimming brings great news indeed.

Nowadays, LED lighting has become a mainstream technology. LED flashlight, traffic lights and car lights everywhere, various countries are pushing for replace with LED lights to the main power supply of residential, commercial and industrial application of incandescent and fluorescent lamps. After the switch to energy-efficient LED lighting, achieve energy saving quantity will be very amazing. Only in China, according to the government when the office estimates that, if a third of the market turned to the LED lighting products, each year they will save 100 million degrees of electricity consumption, and can reduce 29 million tons of carbon dioxide emissions. However, there are still an obstacle to be overcome, it is dimmer.

Incandescent light bulb use simple, low cost at the forefront of thyristor dimmer can easily realize the dimming. Therefore, the dimmers are everywhere. Solid-state lighting replacement lamp to truly achieve success, you must be able to use the existing dimmer controller and circuit implementation.

Incandescent bulb is very suitable for dimming. Ironically, it is their low efficiency and the consequent high input current, the main factor is the dimmers work good. Incandescent light bulb filament in the thermal inertia also help conceal any instability produced by dimmers or oscillation. In trying to move light LED light a lot of problems in the process, often leads to flicker and other unexpected situation. If you want to understand why, first of all, it is necessary to understand the working principle of SCR dimmers, LED lamp technology as well as the relationship between them.

As shown in figure 1 for typical frontier thyristor dimmer, and its voltage and current waveforms.

Figure 1. Cutting-edge silicon controlled dimmer

Adjustment potentiometer R2 SCR (TRIAC) phase Angle, when the VC2 exceeds the breakdown voltage of the DIAC, thyristor AC voltage in each frontier conduction. When SCR to retain its current (IH), thyristor turn-off, and must wait for C2 again next half cycle recharge to conduction. Light bulb filament to the voltage and current is closely related to the dimming signal’s phase Angle, the change of the phase Angle range between 0 degrees (close to 0 degrees to 180 degrees.

Is used to replace the standard incandescent light bulb LED lights usually contains an LED array, make sure to provide uniform illumination. These leds in series way together. Each of the brightness of the LED is determined by the current, the forward voltage drop of the leds is about 3.4 V, usually between 2.8 V to 2.8 V. LED lamp string should be driven by constant current power supply, must carry on the strict control of electric current, to ensure the high compatibility between adjacent LED lights.

LED lights to achieve adjustable light, the power supply must be able to analyze variable phase Angle of thyristor controller output, so that to one-way flow to the LED constant current adjustment. In maintaining the dimmers work is very difficult to do this at the same time, often leads to poor performance. Problem can be characterized by slow startup, flicker, uneven illumination, or flickers when adjust the brightness. In addition, there are inconsistent between components and LED lights emit unwanted audio noise and other issues. This negative situation is usually triggered by mistake or premature shutoff, improper control of thyristor and the LED current caused by factors such as joint. Triggered by mistake when the thyristor turn-on is the root cause of the current oscillations. Figure 2 in the form of charts to illustrate the impact on this.

Figure 2. Level occurs in the LED lamp power input SCR electric current and voltage oscillations

Thyristor turn-on, the AC mains voltage applied to the LED lamp power supply almost at the same time the LC input filter. Applied to the inductor voltage step leads to oscillation. If the dimmer, during the period of oscillation is lower than the SCR current SCR will cease to conduct electricity. SCR trigger circuit charging, and conduction dimmer again. This irregular SCR restart many times, can make the LED lights don’t need the audio noise and flicker. Simpler EMI filter design helps to reduce the unnecessary oscillation. For a successful dimmer, input EMI filter inductance and capacitance must also be small as possible.

Oscillation of the worst conditions characterized by the phase Angle of 90 degrees (at this time, the input voltage peak sine wave, suddenly the input applied to the LED lamp), and for high input voltage (at that time, the forward current dimmer to lowest level). When need depth dimmer (such as the phase Angle is close to 180 degrees) and low input voltage, it will shut off prematurely. To reliably lower luminosity, thyristor must be monotonic conduction, and staying there almost down to zero volts AC voltage point. For SCR, maintain current is usually necessary to sustain the conduction between 8 to 40 mA mA. Incandescent bulb is easier to maintain the current size, but for the equivalent incandescent lamp power consumption is only 10% of the LED lights, the current can be reduced to maintain current below the SCR, lead to SCR early to shut off. This can cause and/or limitation of adjustable light range.

When designing LED lighting power supply and many other problems pose a challenge. Energy star solid-state lighting specification requires that commercial and industrial application of power factor must be at least 0.9 and lighting products must meet the efficiency, output current tolerance and EMI’s strict requirements, and the power supply must also occurs in the LED load under the condition of short circuit or open circuit to make the security response.

Power Integrations (PI) recent technical progress of how to solve the compatibility problem of LED drivers and silicon controlled rectifier to provide the reference sample. Figure 3 is the PI of the silicon controlled dimmer 14 W LED drive circuit diagram.

Figure 3. The isolation type silicon controlled dimmer of general high power factor input 14 W LED drive circuit diagram

This design adopts LinkSwitch LNK406EG – PH series devices (U1). LinkSwitch – PH series LED driver IC and incorporates a 725 V power MOSFET and a continuous conduction mode of primary side PWM controller. Controller can realize single stage active power factor correction (PFC) and constant current output. LinkSwitch – PH series devices used by the primary side of the control technology can provide high precision constant current control (performance is far superior to the primary side of the traditional control technology), eliminating the isolated flyback type optical coupling and auxiliary circuit is commonly used in power supply control circuit (i.e., secondary side), the PFC controller at the same time also save a high capacity electrolytic capacitor.

LinkSwitch – PH series device can be set up to move light or not dimmer mode. For silicon controlled phase dimming applications, can be used in REFERENCE (REFERENCE) on the pin programming resistor (R4) and in the measurement of the VOLTAGE (the VOLTAGE MONITOR) pins to use 4 M Ω (R2 + R3) resistance, kept linear relationship between input VOLTAGE and output current, thus expanding the scope of the dimmer.

Continuous conduction mode has two advantages: reduce the conduction loss (to improve efficiency and reduce EMI characteristics. Reduced EMI characteristics, use smaller input EMI filter can satisfy the standard of EMI. Saves an X capacitor, and eliminate common-mode choke coil or reduce its size. LinkSwitch – PH device built into the function of high-voltage power MOSFET switching frequency jitter can also further reduce the filter requirements. Input EMI filter size means that the drive circuit of resistive impedance is less, its main advantage is that can significantly reduce the input current oscillations. Because LinkSwitch – PH internal reference by its power supply, thus to further enhance the stability. For tunable optical applications, increase the active damping circuit and discharge circuit ensures that the LED lamp in very wide dimming range stable work, without any flashing.

Constant flow control + / – 25% is allowed in the voltage swing, so you don’t need according to the forward voltage drop to encode the LED, and + / – 5% difference still can ensure consistent LED brightness.

This 14 W LED design implements the standard and the thyristor AC dimmer compatibility, extremely wide dimming range (0.5 mA mA: 1000-1500), high efficiency (> 85%) and high power factor (> 0.9). It shows with leds thyristor dimmer related problems can be overcome, and even can simplify the driver design, make the adjustable light LED lamp is more cost effective, and to achieve consistent and reliable performance.
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Low cost simple drive power of high power LED lighting design

Light-emitting diode (LED) has the save electricity and shall not be obliged to frequent maintenance features, has become a street light and other high power lighting application development mainstream. LED lighting driver method is comprehensive, but to meet the market requirement for higher efficiency and lower system cost, a new simple topology circuit to drive more LED lamp string is imperative.

Observe street light or high patio lights for stadium, as well as other application trend of the development of high power lighting, is gradually turning to light emitting diode (LED) as a light source of solid-state lighting, the main reason is that the LED with higher energy efficiency and less frequent maintenance requirements, and these two factors have also proved to definitely have its necessity.

In such high power lighting applications, is considering using a variety of measures to drive the lamp, this paper will discuss a can with a higher efficiency and lower system cost, to drive a new topology of multiple LED lights string. To fully understand the advantages of this topology, the first is currently considering solutions will be discussed, or have a good effect in low power LED application of various methods.

Drive more LED string series strives for efficiency and plan each have advantages and disadvantages

To drive more LED lights string, the simplest method is to use can be converted to direct current (DC) voltage output voltage (12 v or 24 v, for example) of power supply, then to a power drive LED lamp series, in parallel and in each lamp string used in the resistance to adjust current. This method cost is very low, but in today’s high brightness LED will cost more than 350 mA (mA) current, so the loss of this method is great, cause the efficiency is not high, and poor performance of current regulation, and makes the lamp string light very obvious differences between.

If you want to improve this method, linear voltage regulator must be used instead of resistance, in order to enhance all the strings of light output consistency. However, such doing can make the light output is consistent, and efficiency or power did not significantly improve. For the LED to achieve the longest service life, reducing power consumption is very important. In the two methods, the use of resistance or linear voltage regulator as fixed sources of heat, can greatly shorten the service life of LED.

Another also fairly simple method is to make a long single lamp series, series and use can produce high voltage DC stable current source with a single power supply. This method of high pressure operation can reach 60 VDC or 42 volt root mean square (RMS) value security extremely low pressure (SELV) level or above, and the lighting equipment or accessories must go through security agency license, then make the same motor design used in other application flexibility is greatly reduced.

A single lamp string method is another consideration is the reliability. If only one LED on, will release the light output of lighting equipment. Although many arc suppression circuit or device can be mounted to control all the LED to open, but this will increase the cost and complexity of lamps and lanterns.

Using buck converter to adjust current driver circuit to reduce costs as the key

In fact, in the high power LED lighting applications, the most commonly used multiple LED twinkle light of switching voltage regulator to adjust the current architecture, one of the single main power supply will be converted into alternating current (AC) power supply at SELV commonly under the level of a single DC bus voltage; Then, the bus will be parallel LED lamp power supply, and each lamp string have step-down converter (most common) or a boost converter. For simple, in this paper, the analysis is only limited to the step-down converter, because the step-down converter in terms of cost and the number of components with a step-up converter is very similar.

For example, figure 1 shows a simple low cost type step-down voltage regulator circuit, consists of pulse width modulation (PWM) controller, inductance, metal oxide semiconductor field effect transistor (MOSFET), diodes, and multiple resistance and capacitance. If you need more efficiency, can use mosfets instead of a diode, and use can achieve synchronous buck PWM controller.

Figure 1 simple step-down voltage stabilizer

And figure 2 shows using step-down voltage regulator to adjust current of the high power multiple led twinkle light lighting application subsystem block. When the AC power input after rectification, then supply to the power factor correction (PFC) booster circuit, including PFC can produce 400 kv high voltage, and downstream isolation DC – DC converter input power supply. Then, the converter output will be used to produce low voltage bus (normally for 12 v or 24 v), and supply power to after step-down regulation of LED lamp series.

Figure 2 using step-down voltage regulator of general high power LED lighting system

This method has higher efficiency, is the minimum number of LED lamp string form LED lighting ideal choice. However, with more than four lamp series high power applications, component count and cost will increase. For electronic component manufacturers and supply chain, product sales are rising; For lighting equipment manufacturers and users, however, such a high cost for the product is widely used, because of the steady development of solid-state lighting must rely on low cost driver circuit, to let the market forming and stable growth.

Both low cost/high efficiency electrical insulation design bright eye

Figure 3 shows easy (Simple) series input multiple parallel LED drive, this is a very cost-effective multiple LED lights string driven approach. In addition to the PFC, this also is a method of two sections, including reverse stable downstream of the current step-down voltage regulator and DC – DC transformer circuit. The efficiency of this method is quite high, and has excellent light string current regulating function, the most important thing is, it is a low cost way.

Figure 3 simple type drive transformer

In addition, for each lamp string with a single passive circuit of silicon controlled rectifier (SCR) arc suppression, this method can also achieve a redundant utility. If a LED or light string open, the light output is not higher than other light string.

Before the in-depth study of the operation, must first be discussed for more than simple driver transformer is used, it’s problems. Notice first this is electrical insulation design, which can design the secondary side of the output voltage at SELV level the following, need not make lighting equipment combined with the power and interconnection, in order to obtain the permission of the security agencies. Reason and all offline solutions discussed in this article, the power supply still need security permissions, but the lamps and lanterns is does not need to, save a process.

In addition, the output at the level below, can also increase the elasticity of itself, make all sorts of lamps and lanterns can meet the needs of other many lighting applications.

The other from the point of view of thermal management, the insulation design ideal, because there is no metal accessories for LED nearly or contact any of the restrictions. More prominent characteristics is that insulation does not need the output feedback design, reason need not use photoelectric or other safety rated insulation feedback device, therefore, this article will also discuss the simplicity secondary side, because only a minority of secondary side of the passive components, and no bias power supply, active component or control device.

In summary, in terms of operation, simple drive has more than 1% of the perfect matching led twinkle light current, resonant and has a high efficiency operation, can achieve higher with lamp series of the increase in the number of cost efficiency.

PFC circuit output to reduce switching loss

Then the output of the PFC circuit, as reverse step-down circuit input mode, can be configured to generate steady current output, and the system is closed loop near the current, therefore, the current output to the downstream supply to the DC – DC transformer circuit, the circuit consists of one and a half bridge type controller, two MOSFET, capacitance C1 and C2, and a variety of transformers.

Then, the electric current can flow through a half bridge type MOSFET switch, reaching series transformer primary side, among them, the capacitor C1 and C2 will play a lot of functions, not only can be used to establish divider for half bridge type and a resonant circuit at the same time the composition of the component, and is a DC blocking capacitor, helps avoid transformer saturation. And resonant operation allows the MOSFET switch with zero voltage switching (ZVS) switch, this can reduce the switching loss, and force the output diode achieve zero current switching (ZCS), in order to maximize efficiency.

It is important to note that has been converted into AC current of DC current through resonance before and after all the series transformer primary side. Number can be connected in series transformer primary side is quite flexible, because you can choose many transformer winding circle number ratios support or LED lamp series. However, led twinkle light turn ratio should be considered in number, this is because the number of transformer and the forward voltage of each light string.

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