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Powering LEDs in Parallel (With Constant Current Source)

Discussion in 'LEDs and Optoelectronics' started by Gryd3, Dec 31, 2014.

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  1. Gryd3


    Jun 25, 2014
    So... I wound up with a 10A Constant Current source (Cap at 35V Out), and have a few 10W LED modules.
    Each LED module is rated at 700mA with a typical forward voltage drop of 11-14V.

    If I were using a constant voltage source, I would use a current limiting resistor.
    This was not the case, as I dislike the amount of power wasted in heat this way.

    Next solution was a constant current Boost Converter, so I could string the LEDs together... That said, I'm looking to power between 6 and 12 of these LED modules, and would like to avoid sending ~100V down some wiring in an automotive application. (The concern being additional modifications afterward... perhaps someone else tapping into the power line wrongfully assuming it's 12V)

    The solution I half-a**ed thought up was using a lower voltage, higher amperage constant current source, which is described in the first line. The thought was to simply rig my LEDs in parallel with a much smaller resistor to help balance the current flow across the parallel lights. The concern here is two fold:
    -Would a 'current mirror' be acceptable with more than two parallel branches.
    -If one parallel branch were to fail (Open circuit), the remaining branches would then be forced the additional current that the failed branch was allocated... potentially damaging the remainder of the lighting module.

    So I ask:
    Is the Constant current supply something worth working with, or are there better solutions for me?
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    A single constant current source to power parallel circuits is not the best idea. Current distribution will be unequal (worst case: a short in one branch will use all the current provided with nothing left for the other branches). Current sources are fine for series connection.

    For a parallel connection use either multiple current sources or a voltage source that only marginally exceeds the max. voltage of any of the LED modules plus curent-limiting/load balancing resistors (or a local PWM controlled current source for minimum losses)

    Happy new year,

  3. Gryd3


    Jun 25, 2014
    Figured that's where I'd be at, but had my fingers crossed for a trick.
    Thanks Harald. Happy New Year!
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