1W Led Driver

Discussion in 'The Projects Forum' started by lastRites, Apr 19, 2014.

  1. lastRites

    Thread Starter New Member

    Jul 9, 2011
    13
    1
    Hello! A lamp fixture in my living room went bust recently and I cannot find replacements. So I have decided to convert it to LED. I plan on putting 12 1W leds into it. But constant current LED drivers ar a tad on the expensive side and I can't afford them right now. I know I can make some using the lm317 regulators but it would take up space inside the enclosure.
    I have a 12V dc source. Can I run 4 of these 1W LEDs in series? What kind of lifetime can I expect from them? They feel warm to the touch after 10mins on 12.4V.
    I know that this has been discussed here before but I still wanted to sure that this will work :p.
    Regards :)
     
  2. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,172
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    Guesseng Vf @ 2.8V, so 4 LEDs would cutting it a bit close, try 4 parallel strings of 3 LEDs in series with a 10Ω 1W resistor in each of the 4 strings. Around 50,000 hours.
     
    Last edited: Apr 19, 2014
  3. KJ6EAD

    Senior Member

    Apr 30, 2011
    1,425
    363
    Agreed, but use 2W or 5W resistors.
     
  4. lastRites

    Thread Starter New Member

    Jul 9, 2011
    13
    1
    Vf is 2.8V? I thought it was around 3.2. I got the LEDs from a local store. No part number or anything. They came mounted on star shaped heatsinks.
     
  5. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    If you have the LEDs, measure the Vf's, then match them so each string has about same total Vf. The LED's might be around 3.3 V @ 350 mA.
     
  6. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    A simple jig will make measuring easier, Red is LED under test, blue , a white in series with one or 2 diodes like 1N4002. Resistor 25Ω, 5W.
     
  7. Markd77

    Senior Member

    Sep 7, 2009
    2,803
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    Presumably the blue is just an indicator, probably best to give it its own series resistor, because if the DUT is removed with only a 25 ohm resistor it will let the magic smoke out.
     
  8. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    If it smokes it wasn't a 1W white LED. Yhe white 1W LED in series with a diode is for reverse LED connection protection; reversed , pilot LED glows, LED under test - off, correct polarity - pilot off & DUT on & can then be measured. Connecting pilot LED in reverse on initial powerup = poof.
     
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