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

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. 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 _

7. + _ 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 _

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

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

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

11. 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 _

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 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
120vac
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. 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

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 W
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