Transcript Solid-State Lighting - Mercer

LED Drivers
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Al Marble
Manager, Sales & Market Development
January 2010
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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
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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
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Constant Voltage
120vac
Driver
80mA
80mA
Current
Limiter
+
Current
Limiter
24VDC
• 24VDC driver
• 100 watts (max)
• Connect incremental
segments up to max
power rating
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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
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Low Voltage, Constant Current
+
Driver
120vac
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)
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Low Voltage, Constant Current
+
Driver
120vac
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)
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Low Voltage, Constant Current
• When Used
– Small number of LEDs
• Advantages
– Inherently energy efficient
• Disadvantage
– Clumsy with large number of LEDs
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Low Voltage, Constant Current
+
Driver
350mA
350mA
120vac
700mA
• 700 mA driver
• 20 watts (max)
• Like “two 350mA drivers
in one”
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Low Voltage, Constant Current
350mA
350mA
350mA
120vac
1.05A
Driver
+
• 1050 mA driver
• 30 watts (max)
• Like “three 350mA
drivers in one”
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High Voltage, Constant Current
+
Driver
120vac
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)
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High Voltage, Constant Current
• When Used
– High number of LEDs
• Advantages
– Inherently energy efficient
• Disadvantage
– UL considerations in luminaire design
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Constant Voltage vs. Constant Current
All things being equal, constant current is better than
constant voltage due to inherent energy efficiency
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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:

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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 (
)
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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 (
)
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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
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Class 1 vs. Class 2
Expect tendency towards Class 1 due to:
• Economies of running larger number of LEDs
• Potential for greater driver efficiencies
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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
Driver
% Losses = Losses / Input Watts
= 15W / 165W
= 10%
90% Efficiency
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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
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Dimming
vs.
Amplitude Modulation
Current
Current
• Pulse Width Modulation (PWM)
• Dim below 5-10%
• Higher efficiency
• No color shift
• 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
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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
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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
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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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