By BizLED Bureau
Mar 7, 2016: LED driver, a vital component of the LED system, usually gets less attention. However, it is essential for the manufacturers of LED lighting systems to have good knowledge about LED drivers as well.
The new generation sophisticated LED drivers makes it easier for the designers to design LED luminaires more easily. Today, LED drivers are more innovative and intelligent, and hence, enable LED lighting systems more flexible.
Why LED drivers are vital
LED drivers convert any given voltage into a constant current that makes LEDs light up in the desired brightness and color. LED drivers respond to the changing input voltage while maintaining a constant amount of current supply to the LED. They are commonly used for blinking, dimming and color mixing of LEDs in various applications.
As LEDs are available with different power ratings, drivers must produce different constant currents to operate them. Single-watt LEDs require a constant current of 350mA, while 2W LEDs need 700mA. The maximum output voltage of a driver, thus, determines the number of LEDs that can be operated in series. When the voltage is high enough to supply the desired number of LEDs, buck drivers are used. But when the voltage is too low, boost drivers are required. However, in some cases, a combined driver type is needed.
How LED drivers have advanced
The constant pressure to reduce chip sizes and increase lumens per watt has forced manufacturers to come up with modified drivers equipped with the latest technologies, which could further enhance the efficiency of LED lighting and make it more cost effective. They are now coming up with automated features and water proofing/moisture protection and a lot more.
With the recent technological advances, LED drivers have become more innovative, and offer increased flexibility for LED lighting solutions.
Innovative buck/boost driver: An innovative buck/boost driver automatically switches to the correct mode based on the available voltage. When the battery voltage drops below a minimum level of 22V or 23V, the driver automatically switches to boost mode so that the entire battery charge can be used to operate the LEDs. The hybrid LED driver can be connected to an input voltage of between 8V and 36V DC, and provides 2V to 40V DC and a constant current of 350mA or 500mA at the output. Its efficiency is around 92 per cent.
High voltage drivers: Until recently, drivers reached their limit at 40V, so it was not possible to include more than 11 or 12 LEDs in a string. Today, the high voltage drivers can supply up to 17 LEDs in series with constant currents between 350mA and 1200mA. A powerful model comes in a metal casing and provides up to 70W. All drivers of this family can be dimmed in analogue and digital mode. The built-in reference source allows dimming by means of a potentiometer, and also supplies external sensors or controllers for advanced control functions.
Flicker-free TRIAC dimmer: TRIAC dimmers provide a phase-cut sine wave that deteriorates to current pulse if the device is dimmed too much. The two circuits interfere with each other. As there are many TRIAC dimmers installed in homes and offices, and nobody wants to spend a lot of money replacing them when shifting over to LED lighting, engineers have solved this problem by developing a driver that is tailor-made for installation in existing lighting control systems. With such a driver, it is now possible to dim LEDs continuously and without flickering to zero.
What?s latest in the market
ON Semiconductor has launched two new series of power factor corrected (PFC) offline AC-DC drivers for high performance LED lighting applications. The NCL30085, NCL30086 and NCL30088 address single stage design implementations up to 60 W that require high power factor. These drivers broadens the existing solutions which support higher power (up to 150 W) two stage topologies that require low optical ripple and wide LED forward voltage variation.
Mean Well, on the other hand, launched a buck-boost type DC-DC module constant current LED driver?~LDB-L/LW series. The series consists of multiple models of different current levels?300mA/350mA/500mA/600mA. It provides a very wide input/output range, and the drivers can operate perfectly despite the voltage difference between output and input. It has a built-in EMI filter, which enables LDB-L/LW to comply with the lighting standard EN55015. The potted design helps it to work in harsh environments as well. LDB-L/LW series is suitable for street lighting, landscape lighting, tunnel lighting, household lighting, and backlighting.
Inventronics launched 320W constant current LED drivers for lighting applications like high mast, high bay, roadway lighting, arena, etc. EUC-320SxxxDT/ST includes 12 models with maximum output currents ranging from 1.05A to 6.20A, and offers 0-10V dimming. It has an efficiency of 93-94% and provides a 12V auxiliary output and dim-to-off capabilities, making it possible to operate with a wide variety of sensors and controls. These products operate over a 90-305Vac input range and provide excellent power factor correction.
The LED driver is an integral part of any LED-based lighting system. While the life of an LED package may be long, that of the driver may be much shorter, thus reducing the life of the entire system. Since there are a number of brands competing in the market, buyers may face difficulties in choosing the right kind of LED drivers and controllers. The drivers and controllers should be able to work in extreme conditions, especially at high temperatures. Hence, they should consider the following:
Reliability of LED driver: Mean time between failures (MTBF) ratings are a measure of the reliability of an LED driver. Reliability is a measure of how many failures can be expected to occur in a group of units over the lifetime of the product. An MTBF rating of 3 million hours means that you can expect one failure for every 3 million driver hours of operation. A product cannot be expected to last longer than its design lifetime regardless of how high its MTBF rating is.
An LED driver?s reliability also depends upon:
- The number and quality of components used within the driver design
- The rated wattage of the LED driver and the maximum operating temperature of the electrolytic capacitors
- The overall efficiency of the AC-DC and DC-DC stages of the driver
- A suitable thermal management system for the driver such as an aluminium case or forced air cooling fan
- Good driver design where component placement is determined by both safety, EMC and thermal considerations
- The ambient operating temperature where the driver is used
Lifespan of LED driver: Studies have shown that the electrolytic capacitor used in switch mode power supplies often has the shortest life of all components in the system and determines the electronic driver?s lifetime. As an electrolytic capacitor degrades, its capacitance decreases and its ESR increases, contributing to the increase in the current output ripple of the LED driver.
While making a purchase decision, some other aspects also need to be checked. A key factor should be kept in mind, that is, whether the product is the constant current type or constant voltage type. It is also very important to consider the climatic conditions of the place where it would be used.
Other factors that one should look for are the low voltage and high voltage protection, and isolated and non-isolated technology. If one buys an LED driver as per the requirements, then it can help in cutting power consumption.
Opinions expressed by BizLED contributors are their own. None of the facts and figures mentioned in the story have been created by BizLED.co.in. BizLED is not responsible for any factual errors.