Why is my led flashing?

Discussion in 'General Electronics Chat' started by tbfunk, Sep 9, 2016.

  1. tbfunk

    Thread Starter Member

    Dec 9, 2010
    I bought some cheap 3 watt LED's from china and when I hook them up to a 625mA current source they eventually start flashing.
    I have never dealt with high power LED's before however I don't think they flash unless the power source is causing them to do so, right?
    Alternatively if for some reason I may have damaged an LED accidentally through over voltage/current could that cause this strange behavior?

    I am using an LM317 (also cheaply bought from china) to regulate current to 625mA, is this too low or high? I had trouble finding information on the ideal amount of current to use.
    LEDs: http://www.aliexpress.com/item/100P...2320568428.html?spm=2114.13010608.0.77.aeZpfA
  2. Kjeldgaard


    Apr 7, 2016
    With the little information, I can only guess at a thermal problem.

    How fast is the flashing?
    How high input voltage?
    What is the LED and LM317 temperatures? (Be careful not to burn your fingers)
  3. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    What is the voltage/current rating of the source supplying power to the 317? If it's being overloaded it may go into self-protect mode.
  4. dl324

    Distinguished Member

    Mar 30, 2015
    What is the voltage and current rating of your power source? What is the LM317 suffix? K, T, L??
    Use a variable current source to determine an optimal current experimentally. Increase current slowly until you don't notice a significant change in brightness, but make sure you don't exceed 3W of dissipation.

    Electronic components from AliExpress are of unknown source, quality, and reliability. I only buy from there when quality and genuine parts aren't required, e.g. for wires and such.
  5. DickCappels


    Aug 21, 2008
    The thermal shutdown on the LM317 oscillates some/all of the time. You probably need to reduce the input voltage or get a better heatsink. (You DO have a heatsink, don't you?)
  6. ci139


    Jul 11, 2016
    Last edited: Sep 9, 2016