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LEDs in parallel are better?

Discussion in 'LEDs and Optoelectronics' started by eem2am, Feb 14, 2013.

  1. eem2am

    eem2am

    414
    0
    Aug 3, 2009
    Hello,

    Recent advances in LED technology mean its now easier to get the forward voltages of batches of LEDs very similar. Thus the LEDs can be placed in parallel, as long as thermal coupling is good.
    Since the switch mode drivers for LEDs in parallel can be made much cheaper then those drivers for long series chains of LEDs, you generally get more value for money with parallel LEDs.

    So do you know of off-the-shelf LED luminaires which contain parallel LEDs? I wish to buy them.


    (-I am referring to LEDs in parallel but with no series resistors.....these now not being needed with modern, equal Vf LEDs)
     
    Last edited: Feb 14, 2013
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,206
    2,695
    Jan 21, 2010
    Look at COB or indeed many of the higher wattage LEDs. You'll often find this arrangement. The COB LEDs are typically composed of a collection of LEDs in series parallel, mounted on the thermally conductive substrate and without any resistors.

    Equal Vf is an issue, but thermal coupling is the big one. You clearly need to use a LED which can be mounted on a heatsink (so no all-epoxy cases).

    Remember that in such a case, if you connect all the LEDs to a long heatsink, you can destroy the LEDs by providing additional cooling to one end of the heatsink (for example by having it half in shade, half in sunlight)

    Using a higher voltage so all are in series is *much* better. If you can't quite do this and have several strings of LEDs in series, then you should interleave the strings so that localised heating affects all strings as closely as possible.
     
  3. eem2am

    eem2am

    414
    0
    Aug 3, 2009
    thanks, i also look at the SD24 product, this has three parallel strings of eight leds...so 24 leds in total.....just imagine trying to do that lot in series from a 12v input, -the driver would be far more expensive....sometimes the 24 leds are blue.

    (The SD24 does have series resistors, but only tiny 1206 ones.)

    LED current (in each led) when on is 150mA......SD24 is ususally used as a flasher.
     
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