LED driver

Discussion in 'General Electronics Chat' started by JohnUK21, Dec 26, 2014.

  1. JohnUK21

    Thread Starter New Member

    Dec 23, 2014
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    0
    I want to replace the LED driver of a fitting that has a consumption of 15 w

    They gave me a driver with an output of 23-28 V with 500mA constant current

    This has an output of 11.5 to 14w. When I asked them if it is correct they said that the driver has a power factor of 0.9

    And 14w/0.9=15.5w

    So they declare the driver 15w

    I'm confused . Please someone help!
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Dont worry about the driver; worry about the LED.
    What are the LED ratings?
    LED Voltage?
    LED current?
     
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  3. JohnUK21

    Thread Starter New Member

    Dec 23, 2014
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    Thank you mike!!

    I have to check the led specs

    However how is the power factor related and they declare the driver 15w?
     
  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Usually, it is the efficiency that matters; not the power factor...
     
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  5. #12

    Expert

    Nov 30, 2010
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    Sounds like, "Baffle them with BS". An LED is not a reactive load, so power factor has nothing to do with it.
     
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  6. ian field

    Distinguished Member

    Oct 27, 2012
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    If you take power factor to indicate the difference between resistive & reactive loads, then you might get away with that.

    A string of LEDs with a limiting resistor would only draw current when the sum total of Vfs were exceeded by near the peak half-cycle - this is pretty much what common usage takes PF to mean nowadays.

    Similarly, a SMPSU only takes blips of current at the crests of the sinewave to replenish the charge on the reservoir capacitor.

    AFAIK; anything over 50W must have a PFC front end - this is usually a boost converter, on the mains bridge rectifier; the reservoir cap is replaced by a much smaller foil cap as filtering, the current pulses drawn by the boost converter more or less track the instantaneous value of the mains sinewave.

    The boost reg charges the reservoir electrolytic for the main SMPSU section - in a UK 220V unit the reservoir cap would typically be rated 450V.
     
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  7. #12

    Expert

    Nov 30, 2010
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    This thread seems to be about 15 watts, and if you try to use power factor to get there, you have me stumped. However, thanks for the information. I learn something almost every day here.
     
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