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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 l.jpg

LED Drivers

Al Marble

Manager, Sales & Market Development

January 2010


Topics l.jpg
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 l.jpg
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 l.jpg

120vac

Driver

Constant Voltage

24VDC

+

80mA

80mA

  • 24VDC driver

  • 100 watts (max)

  • Connect incremental segments up to max power rating

Current

Limiter

Current

Limiter

_


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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


Low voltage constant current l.jpg

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)

_


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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)

_


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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


Low voltage constant current9 l.jpg

350mA

350mA

120vac

Driver

Low Voltage, Constant Current

+

700mA

  • 700 mA driver

  • 20 watts (max)

  • Like “two 350mA drivers in one”

_


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1.05A

350mA

350mA

350mA

120vac

Driver

Low Voltage, Constant Current

+

  • 1050 mA driver

  • 30 watts (max)

  • Like “three 350mA drivers in one”

_


High voltage constant current l.jpg

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)

_


High voltage constant current12 l.jpg
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 l.jpg
Constant Voltage vs. Constant Current

All things being equal, constant current is better than constant voltage due to inherent energy efficiency


Ul class 2 l.jpg
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 l.jpg
    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 l.jpg
    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 217 l.jpg
    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 l.jpg

    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


    Life expectancy l.jpg
    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 l.jpg

    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


    A few other driver features l.jpg
    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 features22 l.jpg
    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 l.jpg
    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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