Posts Tagged ‘LED driver’

LED Lighting Sees Improvements with The Addition of Hybrid Capacitors

25 Nov

A liquid of gadgets containing light emitting diodes, or LEDs, provides a larger chance for effective and permanent technology in the solid-state lighting industry. Applications add off-grid road signage, medical devices, grassed area lighting and vehicles. With a brighter output, longer life, descend expenditure of power and small to no compulsory maintenance, LEDs are a much-improved lighting choice over illuminated bulbs. When powered by a technology called hybrid capacitors, the benefits of LED lighting are usually furthered.

Hybrid Capacitors Provide Long-term Energy

A multiple of an ultracapacitor and a lithium-ion battery, hybrid capacitors are an preferred choice to power LEDs, that have splendid outlay with low submit power. Because of the low appetite and power of LEDs, hybrid capacitors are a longer tenure appetite source than other substitute appetite storage solutions on the market. They give for more appetite storage with an appetite firmness up to 115 percent more than typical electric double-layer capacitors (ELDCs).

Before hybrid capacitors became available, appetite storage options for LED lights were paltry to rechargeable batteries. These were not ideal, given the batteries could not encouragement far-reaching heat ranges and did not function as they should in impassioned prohibited or chilled conditions. A second regard was that batteries had a comparatively partial life span. For example, LEDs used in grassed area lighting lasted for an median of two years. Because the batteries are not replaceable, consumers had to buy wholly new lighting systems.

Consumers sought a answer with a rapid recharge, high power and long life. Hybrid capacitors compromise the shortcomings of batteries and enable engineers and manufacturers to encounter the final of their customers. Hybrid capacitors moreover enable for power to be granted for an lengthened amount of time given LEDs do not need a high amount of power. With an lengthened life span, the device requires small to no maintenance, that saves time and reduces cost. An updated gain is that without a battery, there is no environmental damage stemming from ordering of polluted materials.

LEDs Well-suited for a Variety of Applications

Hybrid capacitors give more than 20 times the motorcycle life and 60 times faster recharge rates than nickel cadmium or lithium-ion batteries, that severely improves the appetite outlay of LED lighting. With these benefits, LEDs are expected to be used in a far-reaching operation of attention applications.

Hybrid capacitors give faster and more effective power to LED lights used in medical devices. Manufacturers can right away henceforth pattern LEDs powered by hybrid capacitors in to medical devices. With a motorcycle life of 10 years, the hybrid capacitor will typically exist that of the device. These gadgets see charging times as swift as 60 seconds, and sufficient power is generated to last the whole day without a recharge.

LEDs are moreover used in crisis lighting on the roads. During a power outage, safety lighting requires an off-grid answer to work. During daytime hours, solar cells are used to takeover solar energy, that is then converted to physical phenomenon and stored in the hybrid capacitor. When the power is out, the hybrid capacitor automatically provides the stored appetite to power the LED lighting.

With updated benefits of marked down appetite use, increased gas mileage and minimal maintenance, LEDs are replacing normal light bulbs in automobile headlights and taillights. Hybrid capacitors can give the indispensable power to LEDs in crisis situations when there is no other power source available.

Another familiar use of LED lighting is in corridor and grassed area lighting. This includes blurb applications such as crosswalks, sidewalks and medians, together with residential uses in patios, pool decks and landscaping. LEDs give a available solution, as they do not must be transposed due to the hybrid capacitor’s lengthened life span.

By incorporating flashing light in to the LEDs, manufacturers can use them for a few of the above mentioned applications in an attention-drawing manner. This includes exit or end signs, warning signs, ad boards, storefront signs, and other musical office building lighting.

Bright Future in Store for LED Technology

Asia has at large integrated hybrid capacitor powered LEDs in to the continent’s lighting sources. The lights are used to give pool, path and corridor lighting, together with musical office building lighting. Solar power is used to store backup power for astonishing power outages in all of these applications.

Further improvements to this technology could potentially outcome in a light tuber that contains a hybrid capacitor already inside, instead of as a backup source. In the box of mislaid power, there would be no extra need for a well-defined backup source to give power, as the hybrid capacitor will automatically take over in the LED bulb. A astonishment to many, this technology wouldn’t require a large enlarge in price.

The embracing a cause of light emitting diodes (LEDs) is on the rise, as makers of flashlights, road signs and medical gadgets look for ways to expand the lifespans of their products. As fascination in LEDs grows, the use of hybrid capacitors will moreover increase. Consumers, medical professionals, business owners, municipalities and others similar to that LED gadgets last longer, assign faster, catch fewer continuance costs, devour reduction power and are more environmentally friendly. Hybrid capacitors are accountable for these benefits, and they make LEDs an popular answer for solid-state lighting.


Brighter LEDs Can Simplify Driver Designs

29 Sep

LED vendors are producing components that can operate at higher drive currents and produce more lumens, and system designers can move to a simpler two-stage driver as the number of LEDs in a fixture is reduced, explains BERNIE WEIR.

Much attention in the LED lighting world has focused on two applications that are at polar extremes; low-power incandescent bulb replacement and high-power street lights. While these applications are ubiquitous and iconic, there is also a range of area-lighting applications – such as parking garages, park lighting, stairway lighting – and outdoor commercial lighting – such as wall packs, wall washers, and security, flood, gas-station canopy and pathway lighting – which are hiding in plain sight. These medium- to high-power applications are ideal candidates for solid-state lighting (SSL), and new LEDs that operate at higher drive currents and produce more lumens are a good match. Designing a luminaire with fewer brighter LEDs can also simplify the driver electronics and ease the task of adding adaptive controls.

The applications mentioned above are a good match with LEDs, because they consume large amounts of power, have high hours of annual use, and are used in public spaces that may not be occupied for many hours, thus opening the door for adaptive controls and dimming that can significantly reduce energy consumption. Beyond energy cost, a driving factor of LED lighting is long life and reducing the maintenance cost of bulb replacement.

Traditionally, the aforementioned medium-power applications have used high-pressure-sodium (HPS) and metal-halide (MH) light sources. HPS light sources are actually very efficient but generate a decidedly yellow/orange light that has very poor color rendering since the light source is nearly monochromatic.

MH sources display better optical characteristics but have slightly lower initial lumen output, shorter lifetime, and higher lumen degradation over the useful life. MH lifetime (measured to 50% failure point of the population) is in the 10-20,000 hour range depending on the bulb design and construction, whereas HPS has typical lifetimes of 24,000 hours.

HPS and MH sources are also limited in terms of adaptive controls and dimming. And most of these area-lighting applications require directional light. Although HPS and MH bulbs have high lumen output, 40-60% of the generated light can be lost in the fixture.

LED life and controls

High-brightness white-LED light sources address many of the limitations of the legacy lighting technologies as they are inherently directional in nature, have very long operating lifetimes, provide white light with good color rendering and, given their instant-on characteristics, are easy to dim across a wide range of light levels.

FIG. 1

Moreover LED performance has been rapidly improving in terms of lumen output and efficacy (lm/W) and over the last few years has been making in-roads into these traditional area-lighting applications.

When white HB-LEDs came on the market, the most common configuration was called a “1W” LED because when it was driven with 350 mA, it typically dissipated around 1.2W given a nominal forward voltage of 3.3-3.5V. Today, widely-available 1W LEDs can generate more than 100 lumens at an efficacy of over 100 lm/W. To generate 5000 delivered lumens a fixture needs on the order of 50 LEDs whereas 18-24 months ago the same application may have required 80-100 LEDs.

To power such a large number of LEDs from the AC line, drivers have typically used a three-stage power-conversion architecture as illustrated in Fig 1. A two-stage constant-voltage power supply implements power-factor correction (PFC) in the first stage, followed by a high-voltage DC-DC converter that generates a safe isolated voltage rail typically in the range of 28-60 VDC.

The fixed-voltage output rail supplies multiple strings of LEDs. A third-stage, a dedicated buck DC-DC LED driver, provides regulated current to each string. Depending on the output of the second stage and the forward voltage of the LEDs, each string might include 8-12 LEDs.

Brighter LEDs

Some LED manufacturers have developed advanced processes and improved LED chip designs that deliver more lumens at higher drive currents while maintaining the same forward voltage. For example, the Cree XM-L is rated for up to 3A drive current and has a very low typical forward voltage of 3.1V at 1500 mA drive current. At 1500 mA and 85°C junction temperature, in cool white, each LED generates 440-475 lm. A fixture that uses just 12 such LEDs would have an output in the range of 5200-5700 lm with a typical load power of around 53W, delivering over 100 lm/W efficacy.

Going from 50 LEDs in the previous example to 12 simplifies the optics but it has a more sweeping impact on the driver architecture. Now all the LEDs can be safely driven in a single string, eliminating the need for multiple parallel DC-DC LED buck drivers. This also improves light uniformity as all LEDs are driven at the same exact current.

To eliminate the third stage, the two-stage constant-voltage LED power supply is replaced with a constant-current LED driver. This provides two fundamental advantages. The overall system efficiency is improved as one power-conversion stage is completely eliminated, and the cost and design complexity of multiple DC-DC converters is eliminated. It also simplifies adding intelligent control as the dimming function can now be integrated in the current-control loop of the constant-current LED driver.

Adaptive controls have been used in indoor lighting for a number of years and involve combining sensors with networked or autonomous microprocessor-based controls to optimize the lighting level to the needs of the environment. Simple examples include adding an occupancy-sensor lighting control to turn off a light source when there is no activity for a prescribed time.

Control scenarios

In area lighting, controls have been mostly limited to on and off at dusk and dawn. But dimming LED light sources is very straightforward compared to HPS and MH light sources that have long turn-on and restart times. LED light sources can be dimmed across a wide range and can rapidly turn on to 100% brightness based on activity or occupancy. In an outdoor park-lighting scene, for example, this means the light along the running path or walkway can be turned down significantly when no activity is detected and instantaneously turned to full brightness if a jogger runs down the trail in the middle of the night.

Fig. 2 illustrates a possible dimming profile through the course of a typical evening. The gray area represents timer-based control and the blue areas indicate those times that the light source is increased to 100% when activity is detected. The energy savings can be substantial since most of the operating hours are at the reduced energy-consumption levels.

FIG. 2

Application trials for such bi-level control performed by the California Lighting Technology Center at the University of California-Davis indicate these control schemes can yield energy savings of as much as 70-90% over traditional HID approaches.

Let’s consider an example of how new high-lumen packaged LEDs can simply the luminaire system architecture and efficiently convert AC power into a regulated current in the 1-3A range (Fig. 3). Such an LED driver design can also incorporate support functions to enable adaptive controls. The addition of a low-cost microcontroller (MCU) opens the door to more-sophisticated control schemes that can monitor ambient light, occupancy/activity sensors, time of day, and day of week to provide appropriate light in a variety of situations while maximizing energy savings.

MCUs and networks add functionality

For centralized control, these smart luminaires can be networked, for example using a power-line-communications (PLC) modem block (Fig. 3). Alternatively, a system can use a wireless interface like Zigbee, a traditional wired interface such as Ethernet, or existing lighting and building controls.

FIG. 3

The block diagram illustrates an AC-DC driver based on a high-efficiency PFC and half-bridge-resonant (HBR) isolated DC/DC step-down controller integrated in the NCL30051 from ON Semiconductor. The basic current-control loop consists of a simple analog circuit which monitors the output current and provides feedback across the isolation barrier via an opto-coupler to the primary-side control IC. The circuit also monitors the maximum output voltage, preventing driver damage in the event the LED string is accidentally opened.

The MCU monitors sensor feedback and network communications to control the light level. Moreover the MCU generates a PWM signal that is used to turn on and off the half-bridge driver, thereby controlling the light level. The PFC block implements a critical conduction mode (CCM) control scheme which achieves high power factor (>0.98 typical) with low harmonic content and is suitable for applications up to 200W.

Efficiency and power factor

This driver architecture can support a wide range of power levels. Fig. 4 illustrates the typical efficiency and power-factor curve of an example driver design based on the NCL30051 driving 2A with a nominal LED load of 55W. Across the 115-240 VAC line-voltage range, the efficiency exceeds 88% and the power factor is greater than 0.94.

FIG. 4

The Cree XM-L LED is ideally suited for this range of current. At 700 mA, it generates 260-280 lm (neutral/cool white). A string of 9 LEDs driven at 2A outputs more than 5000 lm. This lumen level can easily address a range of area-lighting applications such as wall packs and wall washers. Depending on the drive current and LED configuration, this type of driver approach can exceed 90% wall-plug efficiency, as well as supporting a range of dimming methods required for intelligent control.

New LEDs that have high source-lumen capability can greatly simplify the LED driver architecture by reducing power-conversion stages and increasing overall power-conversion efficiency. Adding smart controls can yield further energy savings and opens the door to new capabilities such as constant-lumen-output operation modes. Here, the driver can control the LED current to maintain constant lumen output over lifetime to combat lumen depreciation. Smart dimming-control techniques have an additional benefit of extending the operating lifetime of the LEDs as well as the driver electronics by reducing the average operating temperature.


LED Drivers And Light Sensors Enable Compelling Displays

06 Jul

TAOS has released light and proximity sensors while Supertex and iWatt have launched new drivers to enable compelling LED-backlit displays.

LED-based display backlighting continues to be the largest market for high-brightness LEDs despite the fact that the general-illumination application gets more notice. New LED driver and sensor products from Texas Advanced Optoelectronic Solutions (Taos), Supertex and iWatt promise to enable displays with the latest solid-state-lighting (SSL) technology for optimal image quality and minimal power consumption.

Indeed light and proximity sensing is needed in devices based on LCDs to set the appropriate backlight level for maximum display quality without wasting power when ambient light is sufficient or when no one is present to view the display. Taos is targeting mobile devices such as smartphones and tablets with its new TSL2×72 family, although the company also expects the sensors to be used in computer-display and HDTV applications.

Taos dual-diode sensor

The new products include the TSL2572 family for digital ambient light sensing (ALS), the TSL2672 family for proximity detection, and the TSL2772 family that includes both light and proximity sensors.

To serve in mobile applications, the sensors must work in very bright environments and the new Taos products are designed for use in full sunlight at levels to 60,000 lx and beyond. “Mobile device vendors are continually striving to deliver more compelling products with an improved user experience; therefore, they demand ALS and proximity detection solutions capable of operating in a very wide range of lighting conditions,” said Jerry Koontz, TAOS Director of Marketing.

Taos uses programmable signal-gain modes, including a reduced-gain mode, to boost the dynamic range of the light sensors. Meanwhile the company boosted the signal-to-noise performance and added crosstalk-compensation technology to deliver more-accurate proximity detection. Both sensor types can be used sporadically while remaining in sleep mode much of the time to minimize power consumption – especially important in any battery-powered application.

The sensors work with any type of light source including fluorescent and at virtually any lighting level. Moreover the dual-diode architecture can provide accurate results even when mounted behind glass that can distort the spectrum.

Supertex driver handles six strings

Supertex is also targeting battery-powered, mobile devices with its new six-channel HV9957 LED driver. Moreover, the driver offers fault protection features for over-temperature, over current, and over- and under-voltage conditions.

Supertex 6-channel driver

“By providing superior fault protection, HV9957 offers manufacturers a precise LED driver that can handle difficult fault conditions in individual LED strings,” states Stephen Lin, Supertex Vice President of Marketing. “HV9957 also features sophisticated digital circuitry to provide frequency control, fault protection, and phased dimming that is controllable to very low duty cycles for high dynamic range in today’s LED backlighting drivers.”

The HV9957 integrates a switch-mode boost converter and six individual linear low-dropout (LDO) regulators for precise control of each LED string. The driver circuit can supply 30 mA to each LED string, a level typical of battery-powered designs.

iWatt targets TVs with 32-string driver

iWatt, meanwhile, is targeting both edge- and direct-lit HDTV designs with its iW7032 driver that can handle 32 LED strings. The driver uses what iWatt calls adaptive-switching technology to both reduce power consumption and component temperature. Gyan Tiwary, Senior Vice President at iWatt, said, “By overcoming the thermal problems of driving large numbers of LEDs together, our engineers have made a large contribution towards cutting costs for the dynamic backlighting industry.”

The adaptive-switching technology senses the mismatch of the forward voltage of the different LED strings, and adapts that drive current individually for each. The company says that the technique reduces the driver power consumption by 2-5W relative to competitors. The technique both saves power and reduces the heat generated by the driver that in turns extends LED component life.

A single iW7032 driver can power a total of 480 LEDs with stack voltages as high as 56V. The driver also integrates the MOSFETs required to handle the output current to each string. The IC supports three different pulse-width modulation (PWM) schemes with 10-bit granularity for brightness control.

Strategies Unlimited projects driver market

The LED driver market is certainly a significant one as Strategies Unlimited details in a new report on the LED driver market segment. The research firm (like LEDs Magazine a PennWell business unit) projects that driver sales will grow to $3.5 billion by 2015 from $2 billion in 2010.

Strategies Unlimited confirms that display-backlight applications will dominate the market through 2015. But the firm expects general-lighting to be the next major market mover for LEDs and associated technology such as drivers.


LED Driver IC Market Benefits from Sales of LED TVs and Lamps

29 Jun

Strategies Unlimited says that the market for LED driver ICs will grow at a CAGR of 12% between 2010 and 2015, driven by the demand for LED TV backlights and replacement LED lamps.

LED driver IC sales will reach nearly $3.5 billion in 2015 from nearly $2 billion in 2010, a compound annual growth rate (CAGR) of 12%, according to Mountain View, CA-based market research firm Strategies Unlimited.

These are among the findings in Strategies Unlimited’s new report “LED Driver ICs – 2011.” Sales for LCD backlights will dominate through the period, with growth from edge-lit TVs and monitors. LED lighting applications will be the “next big thing” for LED drivers and driver ICs, beginning with LED replacement bulbs, as a response to improvements in technology and the phase-out of incandescent bulbs.

LED driver IC revenues are threatened, however, by continued integration into fewer ICs, as well as by competition from organic LEDs (OLEDs), compact fluorescent lamps, and other technologies.

Severe price erosion for driver ICs will limit the revenue growth as volumes increase, but new, higher-priced ICs are appearing that reduce the overall bill of materials and also help maintain the average price of the ICs.

Also, AC-LED products minimize the driver and some eliminate the driver IC, but will not have a significant impact on overall revenues through the period, and may even help accelerate adoption of LED lighting.

Lighting market

The production value of drivers for lighting will see strong 40% compound annual growth through the period. The driver is defined as the entire LED circuit, including the driver IC but excluding the LEDs. Innovations in driver design will help take LED lighting mainstream, but the market will quickly shake out those who cannot meet strict goals for dimming, efficiency, power factor, and price.

To meet these goals, large and small companies are bringing innovations to market, such as digital control and novel high-voltage designs. Industry and government are moving toward more standardized specifications that will reduce manufacturing costs and accelerate adoption.

The top 10 LED driver IC suppliers hold more than 55% of revenues, with about 30 IC suppliers and captive manufacturers sharing the other 44%. With the acquisition of National Semiconductor by Texas Instruments, TI is now the number one supplier of LED driver ICs. Winners will be those who can keep delivering innovative products at competitive prices. Fabrication with leading-edge, high-voltage BCD processes and 8-inch (or larger) wafers will play a key role.


How to Choose LED Driver IC

01 Dec

LED has established its unshakable position in the backlighting of portable devices. Even in the backlighting for the large-sized LCD panel, it has started to challenge the mainstream CCFL. In lighting, LED is especially popular in the market due to its highlighted features like energy-efficiency, environmental friendliness, long lifetime, and low maintenance. The driver circuit is a crucial and integral part of the LED. Whether in lighting, backlighting or the display panel, the choice of the technical architecture of the driver circuit must correspond to specific applications.

The LED lighting mechanism goes as follows: when the forward voltage is applied to both ends, the minority carrier and majority carrier in the semiconductor recombine to release surplus energy, giving off photons. The main functions of the LED drive circuit are to transfer the AC voltage into a constant power supply and match the voltage and current according to the requirements of LED devices. Apart from safety need, the LED driver circuit must also include two other basic features:

First, a constant current should be kept as long as it is possible, thus the output current variation is able to be maintained between the range of ±10% especially when the power supply change goes beyond ±15%range. Here are the reasons for having a constant current driver when using LED as the monitor, other lighting devices or backlighting:

1.To prevent the drive current from exceeding the maximum rate and further affecting its reliability.

2.To meet expected brilliance requirements and ensure the color and brilliance homogeneity of each LED.

Second, the driver circuit should keep low power consumption so that the LED system efficiency can remain at a high level.

PWM (Pulse Width Modification) is a traditional light adjusting technology, which uses simple digital pulses to switch on and off LED driver from time to time. The system only needs to supply wide and narrow digital pulses in order to easily change the output for adjusting LED brilliance. The advantage is that the technology is able to provide high quality white light with high efficiency through easy application. But there is a fatal disadvantage: it is susceptible to EMI (electromagnetic interference), sometimes even produces audible noises.

Voltage boost is an important task of the LED driver circuit, divided into two different topological modes, namely, voltage boost via the inductor and charge bump. As the LED is current-driven, and the inductor is most efficient at the moment of current transfer, so the greatest strength of voltage boost via inductor lies in the high efficiency, which can reach 90% if properly designed. However, its weakness is as much remarkable, i.e., strong EMI, which imposes high requirements on systems of telecommunication products such as mobile phones. With the appearance of charge pumps, most mobiles don’t boost voltage via the inductor. Of course, the efficiency of voltage boost via the charge pump is lower than that in the other way.

No matter in lighting or backlighting applications, the product designer has to face the problem of raising the driver transfer efficiency. To improve the transfer efficiency is not only beneficial for portable products to extend standby time but is also an important means to solve the LED thermal dissipation problem. In lighting, the use of the high power LED also underlines the problem of enhancing the transfer efficiency.

LED needs current and voltage stabilizing components at work, which should be featured with high divided voltage and low power consumption, otherwise, the highly efficient LED will lower the overall system efficiency because of high working consumption, contradicting the principle of energy-saving and high efficiency. Therefore, the main current limiting circuit should use highly efficient circuits like the capacitance, inductor or switching circuit with power supply as it is possible to ensure the high efficiency of the LED system instead of the resistor or the series voltage stabilizing circuit. The series constant power output circuit can keep the LED light output constant in a wide range of power supply, but normal IC circuits will lose some efficiency. The adoption of switching circuit with power supply is able to guarantee constant power output with high transfer efficiency under dramatic voltage variation of the power supply.

At present, LED with its luminous efficacy is far from replacing the three band fluorescent lamps, yet LED lights can efficiently work under safety extra low voltage (SELV), for instances, underwater lights in swimming pools or paddling pools, mining lamps. Besides, LED has unique advantages in the direct use of green energy like solar energy, wind energy, or emergency lights. Particularly in light adjusting, LED cannot only realize zero to one hundred percent adjusting, but also maintain high efficacy during the whole adjusting process without hurting the durability, which is a difficult task for gas discharge lights.

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