Constant Current Driver for 30 Watt LED

Discussion in 'The Projects Forum' started by RodneyB, Feb 19, 2015.

  1. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
    633
    13
    I have a 30 Watt LED in the original fitting which looks like one giant heat sink. The LED is still ok but the driver was hit by lightning.

    I want to use the LED and housing But have only one. On the housing it says 24 Volt DC supply.

    If I get the driver wrong I will blow the LED and I have no chance at trying again.

    I have attached a driver I think "may work"

    Thanks

    Rodney
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    You have connedted the LM317 in the wrong way.
    Now you have a 1.25 Volts voltage regulator with a resistor in series to the load.

    Here is how it should be connected according the datasheet:

    [​IMG]

    It will be very inefficient, as all current X the voltage drop will be dissipated by the LM317.

    Bertus
     
  3. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
    633
    13
    Thanks very much for the help. I really don't have any idea how else to do it. The whole fitting is aluminium and I hope that will be enough.

    Thanks again

    Rodney
     
  4. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    Keep in mind that the LM317 will drop about 2 Volts and the resistor an other 1.25 Volts.
    You will need a headroom of about 4 volts for the correct current delivered to the led.

    Bertus
     
  5. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
    633
    13
    So I should use the supply voltage of 20 Volts in my calculations to compensate for this
     
  6. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    If the led needs 24 Volts to work fully, the powersource should be about 28 Volts.

    Bertus
     
  7. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
    633
    13
    ok Thank you
     
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