LED Drivers

L E D D R I V E R S

Al MarbleManager, Sales & Market DevelopmentJanuary 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

L E D D R I V E R S

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Dri

ver

24VDC

120vac

• 24VDC driver

• 100 watts (max)

• Connect incremental segments up to max power rating

Constant Voltage

Cu

rren

tL

imit

er80mA

Cu

rren

tL

imit

er80mA

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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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Dri

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350mA

120vac

• 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)

Low Voltage, Constant Current

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Dri

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700mA

120vac

• 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)

Low Voltage, Constant Current

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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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Dri

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700mA

350mA

120vac

350mA

• 700 mA driver

• 20 watts (max)

• Like “two 350mA drivers in one”

Low Voltage, Constant Current

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Dri

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1.05A

120vac

350mA

350mA

350mA

• 1050 mA driver

• 30 watts (max)

• Like “three 350mA drivers in one”

Low Voltage, Constant Current

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Dri

ver

350mA

120vac

• 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)

High Voltage, Constant Current

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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: 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 ( )

L E D D R I V E R S

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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 ( )

L E D D R I V E R S

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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

L E D D R I V E R S

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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

Driver165W @ 120vac 150W @ 350ma

% Losses = Losses / Input Watts= 15W / 165W= 10%90% Efficiency

15W of heat

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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

• Pulse Width Modulation (PWM) vs. Amplitude Modulation

Cur

rent

Cur

rent

• 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

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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