LED Drivers Al Marble Manager, Sales & Market Development January 2010

Topics What is an LED Driver? Drive Techniques Constant voltage vs. constant current Class 1 vs. Class 2 Efficiency Life Expectancy Additional “Features” Dimming Power Factor Size/wattage Protection (thermal, environmental) The Future Adjustable drive current Feedback (thermal/optical) Software features Communication and Control

What is an LED Driver? Driver = The “ballast” for an LED system Transforms system voltage (e.g., 120, 240, 277Vac) Fundamental purpose : drive the LED array at a specific voltage / current Proper current/voltage/power critical for light levels and life Regulates power to counter system fluctuations Isolate the LED system from the high voltage to reduce shock hazard and increase safety

+ _ Constant Voltage 24VDC Driver 24VDC driver 100 watts (max) Connect incremental segments up to max power rating Current Limiter Current Limiter Driver 120vac _

Constant Voltage When Used When flexibility is required in adding incremental LED segments Historically used with low power LEDs (well under 1W each) Advantages Flexible Disadvantage Losses in current limiters

Low Voltage, Constant Current + 350mA 350 mA driver 10 watts (max) Secondary “floats” to what is connected to driver 1 LED = 3.5V (1.2W) 2 LED = 7.0V (2.4W) 8 LED = 28.0V (9.6W) Driver 120vac _

+ _ Low Voltage, Constant Current 700mA Driver 700 mA driver 20 watts (max) Secondary “floats” to what is connected to driver 1 LED = 3.5V (2.4W) 2 LED = 7.0V (4.8W) 8 LED = 28.0V (19.2W) Driver 120vac _

Low Voltage, Constant Current When Used Small number of LEDs Advantages Inherently energy efficient Disadvantage Clumsy with large number of LEDs

Low Voltage, Constant Current + 350mA 700mA 700 mA driver 20 watts (max) Like “two 350mA drivers in one” Driver 350mA 120vac _

+ _ Low Voltage, Constant Current 350mA 350mA 350mA 1.05A Driver 1050 mA driver 30 watts (max) Like “three 350mA drivers in one” Driver 120vac _

High Voltage, Constant Current + 350mA 350 mA driver 150 watts (max) Secondary “floats” to what is connected to driver 20 LED = 70V (24W) 30 LED = 105V (36W) 120 LED = 420V (144W) Driver 120vac _

High Voltage, Constant Current When Used High number of LEDs Advantages Inherently energy efficient Disadvantage UL considerations in luminaire design

Constant Voltage vs. Constant Current All things being equal, constant current is better than constant voltage due to inherent energy efficiency

UL Class 2 UL Class 2 rating represents compliance with standard UL1310 UL Class 2 rating means output is considered safe to contact and no major safety protection is required at LED/luminaire level UL Class 2 has the following electrical restrictions: Maximum output current: 5Adc Maximum output voltage: 60Vdc (dry); 30Vdc (damp/wet) Maximum output power: 100W Any LED Driver used for Signage applications must be listed in the UL Sign Components Manual As component of an LED system, an LED Driver is not listed but recognized by UL ( )

UL Class 1 LED Drivers with output outside the range required by UL1310 (Class 2) need to comply with standard UL1012 Under this standard, LED Drivers are considered UL Class 1 devices An LED Driver with UL Class 1 rating means its output is considered “high voltage” and safety protection is required within the fixture Fluorescent and HID ballast fall under this category Also as a component of an LED system, an Class I LED Driver is not listed but recognized by UL ( )

Class 1 vs. Class 2 Class 2 Easier to accommodate in fixture design Simpler UL process Electrical restrictions limit number of LEDs per driver Class 1 Allows larger numbers of LEDs per driver Potential for greater driver efficiency (due to high voltage, low current) Added protection necessary in fixture UL process not well understood relative to LEDs

Class 1 vs. Class 2 Expect tendency towards Class 1 due to: Economies of running larger number of LEDs Potential for greater driver efficiencies

Driver Efficiency Driver Same issue as ballasts Typical efficiencies 80-85% for low voltage systems Class 1 affords new efficiency gains High voltage (and hence low current) Losses related to current, so lower current means lower losses 15W of heat Driver 165W @ 120vac 150W @ 350ma % Losses = Losses / Input Watts = 15W / 165W = 10% 90% Efficiency

Life Expectancy 50,000 hr life expectancy common for drivers (matches 50,000 hr useful life of most LED systems) Lots of talk/requests for extended life Yes, longer life can reasonably be expected when operating at lower temperatures Key: Analysis must be done at the luminaire/system level More to the system than just drivers and LEDs Full range of external variables must be considered Evaluation of individual components misses too many details Worthy On-Going Topic: System level analysis to understand and potentially increase life ratings, proceeding conservatively

Dimming Pulse Width Modulation (PWM) vs. Amplitude Modulation Current Dim below 5-10% No color shift Higher efficiency Lower cost Dimming Control Standard 0-10v control will be common for commercial Line voltage control necessary for residential Triac-style dimmers: Some work to be done to make common for SSL

A Few Other Driver “Features” Power Factor…..Greater than 90% With advent of electronic ballasts, this has become a non-issue Size/Wattage Current drivers on market around 150-200W Some luminaire manufacturers use 2 per fixture Larger wattages required? LED efficacy improvements over time may negate need

A Few Other Driver “Features” Thermal Protection Most use common thermal protectors (TP) which open when driver overheats New method now emerging: Thermal foldback Reduce drive current as driver senses overheating Environmental Protection IP66 becoming a common rating (pretty robust) Still require an electrical enclosure and full protection from elements

Future Driver Features? Adjustable drive current Sensing element on LED board that tells driver to operate at certain current Flexibility and forward compatibility Thermal Feedback Sensing element within fixture to tell driver to reduce current Optical Feedback Measure light and adjust over time, or to adjust to desired color mixing levels Software/Control/Communication