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LED Drivers

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

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LED Drivers

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

  2. 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

  3. 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

  4. 120vac Driver Constant Voltage 24VDC + 80mA 80mA • 24VDC driver • 100 watts (max) • Connect incremental segments up to max power rating Current Limiter Current Limiter _

  5. 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

  6. 120vac Driver 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) _

  7. 120vac Driver Low Voltage, Constant Current + 700mA • 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) _

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

  9. 350mA 350mA 120vac Driver Low Voltage, Constant Current + 700mA • 700 mA driver • 20 watts (max) • Like “two 350mA drivers in one” _

  10. 1.05A 350mA 350mA 350mA 120vac Driver Low Voltage, Constant Current + • 1050 mA driver • 30 watts (max) • Like “three 350mA drivers in one” _

  11. 120vac Driver 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) _

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

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

  14. 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 ( )

  15. 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 ( )

  16. 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

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

  18. Driver Driver Efficiency • 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 165W @ 120vac 150W @ 350ma % Losses = Losses / Input Watts = 15W / 165W = 10% 90% Efficiency

  19. 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

  20. Current Current Dimming • Pulse Width Modulation (PWM) vs. Amplitude Modulation • 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

  21. 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

  22. 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

  23. 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

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