LED drivers: The engines behind LED lighting systems
The LED ballast or driver plays a key role in determining the life of a product. 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. Drivers account for nearly 20 per cent of the total cost of the components used in an LED light. With LEDs moving into various application areas, their drivers need to be more efficient and cost-effective.
The Indian LED lighting market generated a revenue of US$ 168.6 million in the last few years and is expected to grow at a CAGR of 38 per cent in the upcoming years. Currently, the LED driver market comprises both imports and locally manufactured products. Domestic companies, however, are setting up plants to manufacture drivers. But the missing link in the Indian ecosystem is local IP capabilities, though design registrations are being encouraged.
Types of LED drivers
The three types of LED drivers are:
• Constant current (350mA, 700mA or 1A) drivers
• Constant voltage (10V, 12V or 24V) drivers
• AC LED drivers
Constant current drivers fix the current, and can vary the voltage. However, this depends on the load of the LED. Constant voltage drivers, on the other hand, require a fixed voltage. The LED loads are added in parallel across the output of the driver until maximum output currents are reached. AC LED drivers are actually no-minimum load transformers, which means that they could technically operate low-voltage halogen or incandescent bulbs as well.
The purpose of LED drivers
LEDs require drivers for two purposes:
• LEDs are designed to run on low voltage (12-24V), direct current electricity. However, most places supply a higher voltage (120V-277V), AC electricity. An LED driver rectifies higher voltage, alternating current to low voltage, direct current.
• Drivers also protect LEDs from voltage or current fluctuations. A change in voltage could cause a change in the current being supplied to the LEDs. The LED light output is proportional to its current supply, and LEDs are rated to operate within a certain current range (measured in amps). Therefore, too much or too little current can cause light output to vary or degrade faster due to higher temperatures within the LED.
Internal vs external drivers
Every LED light source requires a driver. However, some LEDs, particularly those designed for household use, contain internal drivers rather than separate, external drivers. Household bulbs usually include an internal driver because it makes replacing old incandescent or CFL bulbs easier. These include LED bulbs with standard screw-in or plug-in bases or those that specify a linevoltage (120 volts) input on their datasheet.
LEDs that typically require an external driver include cove lights, downlights, and tape lights, as well as certain fixtures, panels, and outdoor-rated lights. These bulbs are often used for commercial, outdoor, or roadway lighting purposes. They typically require a separate driver because it is simpler and cheaper to replace the driver than the LEDs.
Sometimes, LEDs come equipped with a separate driver. Otherwise, the manufacturer’s datasheets will specify whether or not an LED requires a separate driver, along with the type of driver it requires, if necessary.
The lifetime of an LED driver
The driver’s lifetime should be an important parameter that buyers and investors should consider. The longevity of an LED driver is determined by the lifetime of the individual electronic components inside it. The weak link is usually the electrolytic capacitors, which are typically gels that act like little batteries.
The problem arises when these capacitors gradually evaporate over the component’s lifecycle, because of the temperature inside the driver — which, in turn, correlates with the external temperature on the driver case. Higher operating temperatures speed up capacitor evaporation and, hence, shorten its life.
There is a small circle called the hotspot or ‘Tc point’ on the label of most LED drivers, which signifies the hottest point on its surface during operation. Using the driver close to this limiting temperature or Tc point mark shortens its operating lifetime. Operating at a lower temperature ensures better durability.
What’s new in the market
Currently, the LED market has ballasts with a capacity ranging from 3W to 120W and above. The capacity shift depends on the wattage of the LED in which the ballast is being used. At present, there is a constant need to reduce chip sizes and increase the lumens per watt; so manufacturers are continuously working on the drivers to meet these challenges, thus helping to reduce the cost of the final product.
One technology to watch for is Light Fidelity (Li-Fi) as it has been getting a lot of attention lately. This bidirectional, high-speed and fully networked wireless communication technology uses LEDs.
What the future holds
The latest development in the LED driver market is the entry of AC-powered LEDs. These avoid the use of ACDC converters and can be powered directly from the AC mains with minimal driver technology. The future of LED drivers should logically lie in the development of innovative driving techniques for AC LEDs.
With LED systems gaining prominence, the need for standards becomes critical. Presently, the standards
that are important include Energy Star, IEC standards, UL and RoHS.
IS standards have been released, but have not been made mandatory. However, they will soon be applicable. This will help to bring quality products to the consumers and curb imports, which is a major worry for the industry at present.
The importance of selecting the right LED driver
Current can only flow in one direction through an LED (diode). The internal operations that go on in an LED depend on the quantity of current flowing through it. Due to the direct correlation between current intensity and the actions performed, an increase in operations will lead to a rise in current flow, which in turn, will increase the internal temperature. This internal temperature needs to be within specified limits. If these limits are crossed, the LED device will malfunction or fail. This limit/threshold is kept in check by LED drivers. In case the LED driver is not able to contain the current flow within the limits specified, overpowering of the device will render the device useless or permanently damaged.
In case the LED driver does not receive the necessary amount of voltage for its operations, either the LED will not glow at all due to voltage shortage, or even if it does, it may flicker or appear comparatively dimmer than usual. At times, it may also get damaged due to voltage inconsistency. So, cautiousness is required.