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Power led with constant current power supply

Discussion in 'Power Electronics' started by Alex Andru, Sep 21, 2017.

  1. Alex Andru

    Alex Andru

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    Sep 21, 2017
    Hello everyone !
    My name is Alex, and this is my first post on this forum.
    I would like to ask you about about driving power leds with constant current power supply.
    I have read a lot and I am still confused on some aspects.
    For example, if I'm having a 600mA cob which supports up to 36v (for 350mA is somewhere around 33V), what power supply do I need? What happens if I use a 350mA power supply or less? What happens if I use a 600mA supply? Does it need to be 36v or more ? Do I need a resistor ?

    Thank you in advance, and excuse my gramatics. English is not my native language.
     
  2. kellys_eye

    kellys_eye

    4,286
    1,145
    Jun 25, 2010
    Providing the voltage is high enough to drive the LED(s) then all you need is do is chose the correct current.

    If you have a 600mA COB you need a 600mA CC device - a single white LED runs at around 3.6V so a 36V driver can run 10 of them. Or 1, or 2 ..... etc.... but no more than 10.

    If you have a 350mA LED then you need a 350mA driver.

    No resistors are needed.
     
    Last edited: Sep 21, 2017
  3. Alex Andru

    Alex Andru

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    0
    Sep 21, 2017
    Thank you ! I finally understand how it works. I appreciate your answer.
    One more thing: what happens if the power is exceed? For example: two COBs of max forward current of 600mA 36v are powered by a 700mA 36v power supply ? And I'm asking because I used a lamp for a few years made with this specifications and everything was fine. I wonder if the power supply is affected or the leds are running at half power (which is ok, as they will have longer life).
     
  4. kellys_eye

    kellys_eye

    4,286
    1,145
    Jun 25, 2010
    Running them in excess of the stated ratings will reduce their life span - very rapidly.

    Of course, running them UNDER the recommended rating will increase their lifespan! If full brilliance isn't your 'thing' then running them at half power will be fine.
     
    Alex Andru likes this.
  5. BobK

    BobK

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    1,598
    Jan 5, 2010
    A constant current supply will have a compliance range, the range of output voltages over which the current is maintained. Your LED must be within that range.

    For your 36V at 600 mA COB LED, the supply must be a constant current supply of 600mA or less, with a compliance range that includes 36V, and 36V should not be at the top or bottom of the range.

    For example:

    Supply 1: 600 mA 24 to 40V good
    Supply 2: 600 mA 18 to 36V questionable
    Supply 3: 350 mA 30 to 40V good, but less bright

    Bob
     
    Alex Andru likes this.
  6. Alex Andru

    Alex Andru

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    0
    Sep 21, 2017
    Many thanks for the answers ! It's clear now how it works.
     
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