The driver seat of a LED based system, LED drivers performs an important job in controlling performance of overall system. A LED driver allows longer standby-power and increases the safety of the fixture. This is exclusive story bought together major LED drivers manufacturers to present their expert view son trends & technology in LED drivers.
The LED driver acts as a power supply for LED modules, regulating output voltage or current for the light source. It transforms and conditions incoming power (typically AC, but it may be DC) and drives the current to the LEDs. In doing so, the LED driver performs a similar function as a fluorescent ballast.
The driver is a critical component of the LED lighting system. Its design affects operation, presence of flicker, service life, controllability and ability to withstand power surges. The overall trend is towards greater functionality.
The driver is a critical component of the LED system, acting as the power supply and providing controllability, ability to withstand transient voltages, and, in programmable drivers, tuning and intelligence. Specifiers should pay attention to the manufacturer and features of the driver to ensure the lighting product provides reliable performance in its intended application. LEDs are driven by constant current (350mA, 700mA or 1A) drivers or constant voltage (10V, 12V or 24V) drivers. Constant current drivers fix the current of the system and vary the voltage depending on the load of the LED. Constant voltage drivers require a fixed voltage and the LED loads are added in parallel across the output of the driver until maximum output currents are reached.
Topologies for LED Drivers
As LED backlights continue to displace CCFLs in LCDs, display manufacturers have to deal with several important decisions regarding the choice and arrangement of these LEDs and how best to drive them. One major decision is whether to use a large number of low-power LEDs, or a smaller number of medium- to high-power LEDs. The use of low-power LEDs results in a lower cost per LED, but requires a higher quantity of LEDs to properly backlight the LCD. The electrical configuration of these LEDs is also critical because some configurations can lead to impractical, expensive, or inefficient driver designs. With the use of medium to high-power LEDs, the driver electronics are more simplified, but the optics can become more challenging, requiring more elaborate schemes to turn a small number of point sources into a single, uniform backlight. In order to properly drive the wide variety of LED backlit panels available on the market now, electrical design engineers will need to successfully implement one of the many LED driving topologies available. Some of the important topologies in LED drivers are:
Buck Converter
The simplest switching conversion approach is to use a buck converter – it has the lowest component count, a very simple (low cost) magnetic component (an inductor) and the highest efficiency.
The use of single stage combined PFC and CC controllers means that for PFC and low ATHD, buck converters are still a viable choice for non-isolated designs. Buck converters of this type cannot provide functional isolation. For buck conversion to work, the input voltage needs to be higher than the output voltage. The latter issue is important when considering ATHD in the newest generation of combined PF and CC drivers (see above). It can be shown that in order to meet EN61000-3-2 C/D standards for THD, the output voltage from a lowline input buck converter must be less than approximately 35 VDC. This limit is needed to keep the conduction angle (the proportion of the switching cycle over which the switching circuit is able to conduct and therefore influence input current wave-shape) high enough to effectively shape the input current to meet THD limits. For high-line applications the maximum output voltage is approximately 70-75 V.
Buck-Boost Converter
Buck-boost conversion is the next alternative – component count is similar to buck design sand efficiency is also very high. Buck-boost converters operate across a wider portion of the available conduction angle and so can provide good THD for higher output voltage designs. They have a similar problem with isolation and duty cycle limited input/output voltage ratio as buck converters.
Tapped-Buck Converters
The next category to consider as a possible solution is tapped-buck converters. The more complex winding structure of the magnetic element introduces a cost and efficiency penalty. However the transformer/inductor nature of the winding structure allows a turns-ratio type adjustment of output voltage and current making tapped buck converters good for standard designs where the input to output ratio precludes the use of a buck or buck-boost topology. It is appropriate to consider the tapped buck converter as analogous to a non isolated flyback converter.
Flyback Converters
The final category of LED driver we will consider is the flyback converter. The converter can be implemented as either isolated or non-isolated and the turns-ratio capability of the transformer allows for pretty much any ratio of input to output voltage.
Due to imperfect coupling between primary and secondary windings, as well as primary parasitic capacitance, the more complex winding arrangement leads to increased cost and power losses. Flyback converters are overwhelmingly used for isolated LED bulb designs and use either a passive-valley fill PFC circuit (Valley fill is acceptable for 0.7 PF applications but induce 8-10% efficiency penalty in reaching the 0.9 PF required for commercial applications), or higher efficiency combined CC and PFC converters that are available today.
Mr. Youvraj Chandrakar, Head, Power Management, Multimarket, Infineon Technologies India
In views of Mr. Chandrakar, today the lighting industry is in a state of change transitioning from traditional lighting sources to efficient lighting with LEDs. LED driver plays an important role in LED system to highly enhance reliability, energy efficiency and performance by selecting suitable discrete switches and controller to enable this significant change. This conversion presents the lighting industry as a whole with a series of challenges e.g. Compatibility of LED retrofits with existing infrastructure, accelerated product life cycles, increasing R&D cost etc.
Infineon offers solutions and semiconductor products based on a deep understanding of the application needs of lighting customers, our range of products & solutions focusing on:
– Low-cost LED driver ICs for LED retrofit lamps
– High efficient LED drivers in commercial indoor & outdoor lighting
– Comprehensive portfolio of high-voltage MOSFETs
– Microcontrollers with dedicated peripherals for intelligent lighting
By the way, a flexible design is also trend for a general platform to reduce the LED driver customer’s inventory. For example, using Infineon’s ICL5101products to design wide voltage output and wide current range LED ECG can meet various end customer requirement in a single platform.
Infineon recently launched new generation of power devices like CoolMOS, GaN, to enhance energy efficiency and power density. The new CoolMOS CE series is cost optimized platform for price sensitive application and new combo IC ICL5101which integrates PFC and LLC resulting in a low external component count and total cost.
Easy design to short development cycle. The newest digital Power 2.0 technology will be also applied to coming high performance lighting with friendly design interface for fully configurable protection modes and set up dimming mode easily which will benefit customers to easily realize intelligent lighting and fast response to market requirement.
Mr. Yoshiyuki Kato, Director Lighting, Anchor Electricals Pvt. Ltd.
As per Mr. Kato, one of the biggest features of LED system would be a longer product operating life.
LED itself might be able to last long as it is, meanwhile the other related components such as LED drivers may not necessarily do so. It is hence very important to design the drivers correctly to deliver optimum reliability while lighting up a space. Furthermore, LED drivers are responsible for the quality of light over the LED light sources. The constant current control is well-known used for LED driving and the quality is directly reflected to the QOL. The current stability and small HF ripple are the major characteristics to maintain the QOL.
Likewise, in order to achieve excellence of LED system, we have to choose the right LED driver over the LED light source. As fundamental requirements of LED drivers in addition to those, high efficiency, safety certifications or RoHS compliance should be considered. Talking about new trends influence designing of LED drivers, he said the major ones are:
- Color control: By utilizing two or more different color-mixed LEDs in arrays, the LED driver controls the output current and consequently controls the color output from the LED light source. It’s known to be comfortable for human when the color of light follows to a black-body locus. The LED drivers have to control the tracks as the LED system wants.
- Flexible current tuning: Customers would always like to optimize their light output. In such cases, the
LED drivers are able to offer the flexibility to change the light output as per the customer needs. The conventional dimming function can support this feature. However, the latest tuning technology can accept to change the output without dimming signal, which conventional one cannot. It gives customers more flexibility to change their light output anywhere, even after the installation. The efficiency of LED is getting better day by day. Thus, this feature may be useful to tune the light output when the LED light sources are replaced.
He further added on new innovations, Wireless control adaptable following smart-phone technologies, a wireless control such as Internet Of Things (IoT) is getting popular in all over the world.
The trend also comes into a lighting business field, from residential to the outdoor markets. It can pave a way to foster large scale saving t by controlling the light source interactively and wirelessly. It would be also connected to the lighting sensors, like occupancy sensors, timer-controlled sensors, or daylight controlled sensors. Driver on Board (DOB): Enhancing to the down-sizing, the LED drivers might sit on the board next to the LED Light source, although the current drivers are separated and placed in another independent box out from LEDs. It would allow them to utilize the LED light sources simpler, like no driver necessary. Less numbered components are the key to achieve the technology.
Mr. Harmeet Singh, Technical Lead, Analog Applications, Texas Instruments India
Mr. Singh shared with us his views as, LEDs are becoming the de facto light source in today’s world of ever expanding applications. They offer various advantages such as longer lifetime (average lifespan of > 100000 hours), increased energy efficiency and better color properties compared to any other light source available as of today. But LEDs cannot produce light on their own. Normally they require dc power of 2-4Volts with few milli amperes of current for optimum operation. They should be driven with either constant voltage or constant current to give light output. The critical part is that variation in either of the above on the plus side can result in more current flow through LEDs resulting in increased temperature, thereby decreasing the lifespan of the LEDs. On the other side, variation on the negative side will result in decreased light output from the LEDs. The component called the LED driver comprises of a power electronics circuit which converts the available 220V /110V AC source into DC power source for driving LEDs. The driver isolates the high line voltage source along with its fluctuations from the LEDs thereby regulating power supplied to them. An LED driver is the power supply for LEDs just as ballast is for fluorescent lighting system. All the advantages of LEDs mentioned above can be negated in an LED system if the driver is not able to do its job efficiently. LED drivers are designed with the following specifications taken into consideration in order to create a successful LED system.
- High efficiency resulting in more light output with less power consumption, thereby resulting into lesser heat and eventually, better reliability.
- High power factor helps the utility station in managing the power efficiently
- Low cost results in the overall cost reduction of an LED system thereby encouraging consumers to use them.
- Fewer parts in design help in improving reliability.
Talking about new trend he said, LED drivers are a lot more adjustable and hence adaptable to our ever changing needs. Apart from normal applications – bulbs, tubelights, downlighters, street lights, etc., LED drivers are showing a variety of upcoming trends. The newer one seems to be available with value added features such as dimming, tunable or programmable, mixing or sequencing of colours, remote controls capability and much more. With Dimming LED drivers, LEDs can be used to create a certain ambience, or to highlight certain features. It is a misconception that dimming results in loss of energy, it is the opposite which is true. Dimming though results in a slight decrease in efficiency of the driver, results in significant energy savings. The life span of LEDs is also improved if they are operated at lower temperatures. LED drivers which are compatible with conventional 0 to 10V analog dimmers or phase control dimmers are available nowadays. In an analog dimmer, 10V implies LEDs being switched ON at the highest brightness level and 0V means that the LEDS are at 5-10% brightness level of fully switched ON condition. Phase control includes two types –one compatible with leading edge or triac dimmer which is the most common type available in market and the other compatible with Lagging edge or transistor dimmer. The triac dimmer has the issue of generating EMI (Electromagnetic interference) while the lagging edge is more expensive although generating less EMI. Apart from these LED drivers are coming which are compatible with digital addressable remote lighting interface (DALI), a wired communications protocol which was applicable for fluorescent ballasts originally. The interface allows users to program their LED fixtures using digital signals to send control information to each LED light. User can set different lighting and ambient levels for each display as per their needs. LED drivers are now becoming smart with wireless controls added which can be operated by remote, mobile applications and even through our voice .Protocols supported are Zigbee, 6LowPAN, ZWave, WiFi and Power Line Communication. LED drivers are becoming intelligent with embedded sensors such as occupancy, photo and thermal.
LED drivers with photo sensors maintain a light level consistent with daylight. As natural light enters a space, the driver dims the LED light and when the sun goes down or on a cloudy day, the light level is increased. The drivers with embedded occupancy sensors go a step beyond scheduling by detecting motion with a space and switching the LEDs on and off as per requirement. Thermal sensors in LED drivers help in a thermal foldback feature. LED drivers in this case, dim the lights if the temperature of the LED casing increases beyond a threshold level to protect it. Thus the system will keep on giving less light output instead of completely reducing or blocking the light flow. Color- Sequencing or changing is the also the popular feature coming in recent LED drivers. This is implemented by dimming a mixture of colored LEDs in an array to change colors. Another option is that the LED driver output is converted into three channels for driving three types of LEDs – red, blue and green – which is mixed to create a millions of colors. Additionally with a sequencer user can generate a preset sequence with color changes occurring at a user set speed. Tunable drivers are a ‘happening phenomenon’ in the market nowadays, a highly demanded one being architectural lighting. In tunable, the manufacturer provides the option of setting the
current output level as per the need of the LED configuration. Thus these drivers give the flexibility of using a single driver for multiple LED configurations. Another variant of these tunable drivers are with the feature of maintaining constant light output throughout the life cycle of LEDs. Normally the driver current is set to 80-85% of the maximum output current capability or by dimming set it to the desired level. As LEDs age, the light output from them decreases so the customer has the option to increase the current or decrease dimming to tune it again to the original light output. What latest from TI, he said, from the glow on your smartphone display to brighter car headlights, TI’s technology drives LEDs in applications to illuminate your path, life and world. Extensive portfolio includes AC/DC, DC/DC, LED drivers, power management devices, wireless and wired interface control and embedded processors for general/smart lighting, signage, backlighting and automotive applications. To meet the need of manufacturers to have greater flexibility in their choice of wireless technology for industrial applications including lighting, TI has created the SimpleLink ultra-low-power microcontroller (MCU) platform. The architecture is based on the ARM® Cortex®-M3 and currently offers memory configurations from 32 KB up to 128 KB Flash. What makes the SimpleLink platform unique, however, is its scalability across wireless technologies. Devices support a range of different radios with pin-to-pin compatible package options, including Bluetooth Smart, Sub-1 GHz, ZigBee, 6LoWPAN, IEEE 802.15.4, RF4CE™ and proprietary modes operating up to 5 Mbps. All 2.4 GHz technologies and all Sub-1 GHz technologies are directly pinto-pin compatible. The first two devices available in the SimpleLink ultra-low power platform are the CC2640 for Bluetooth Smart and the CC2630 supporting 6LoWPAN and ZigBee. Additionally, the platform supports both ZigBee RF4CE with CC2620 as well as the Sub-1 GHz operation. For the ultimate in flexibility, TI has announced the CC2650 multi-standard device. This “superset” device can be dynamically configured in both hardware and software to support one of several different 2.4 GHz radios. Designs built with the CC2650 can go to production without locking in a selection and be configured at the time of installation in the field. TI’s digital Ambient Light sensing devices help customers implement self-dimmable Lighting solutions thereby making them as efficient as they can get. The OPT3001 is a single-chip lux meter, measuring the intensity of light as visible by the human eye. The precision spectral response and strong IR rejection of the device enables to accurately meter the intensity of light as seen by the human eye regardless of the light source.
Conclusion
LED driving market is very prospective in India driven by the factors like, huge market of fluorescent lamps to be replaced by LED lights and favorable Govt. policies.
