How to power backlit LED's?

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  • Pioneerx01
    Badcaps Veteran
    • Apr 2015
    • 241
    • US

    #1

    How to power backlit LED's?

    I was given several backit LED strips from TV's, but no other components (like these). I was told that they came from working TV (LG 49LB5550). I am trying to power them on. I tried 6V, 12V and 24V, but I can't get them to turn on. What are they running on 48VDC, 120VAC something else?

    Thanks
  • stj
    Great Sage 齊天大聖
    • Dec 2009
    • 30965
    • Albion

    #2
    Re: How to power backlit LED's?

    does it have connectors at both ends?

    Comment

    • Pioneerx01
      Badcaps Veteran
      • Apr 2015
      • 241
      • US

      #3
      Re: How to power backlit LED's?

      Yes the connectors are there, They are still technically in the metal back assembly of the TV.

      Comment

      • japlytic
        Badcaps Legend
        • Oct 2005
        • 2086
        • Australia

        #4
        Re: How to power backlit LED's?

        Although I cannot see the picture, the LED strip would most likely require a proper driver circuit.
        My first choice in quality Japanese electrolytics is Nippon Chemi-Con, which has been in business since 1931... the quality of electronics is dependent on the quality of the electrolytics.

        Comment

        • stj
          Great Sage 齊天大聖
          • Dec 2009
          • 30965
          • Albion

          #5
          Re: How to power backlit LED's?

          the led's are in series,
          if the strip has connectors at both ends you first probably want to connect the pins together at one end to create a loop.
          then you need to feed the other end with (led's x 3) v
          so if it's 10 leds - 30v
          that should get something.

          Comment

          • mariushm
            Badcaps Legend
            • May 2011
            • 3799

            #6
            Re: How to power backlit LED's?

            Look at the traces and see how many leds are connected in series. Each led requires about 3-4 volts, but it could be more, depends on how each led is manufactured.

            It's common for such light strips to require about 60-80v to drive the leds, and usually there's 2 or 3 or more segments of leds each powered from voltages up to 60-80 volts.

            Your strip may be made out of two segments, since you say there's a connector on each side. I wouldn't connect the pins together for a loop because you may just short the negative and positive leads that way, just look at the pcb and follow the traces first to figure out how the leds are connected.

            Note that you can't just power the leds from a regular power supply (whatever voltage you decide on), you'll burn the leds due to too much current. You need to limit the current going into a reasonable value. Start with something like 20mA, then move on to 50, 75, 100mA etc

            You can do that by putting a resistor in series with the power supply ... Use V = I x R and P = IxIxR formulas to figure out resistor... for example if you think the leds need 40v to work and you have a 48v power supply and you want to limit current to 20mA (0.02A) then
            48v - 40v = 0.02 x R so
            8 = 0.02 x R ===> R = 400 ohms and

            P = 0.02x0.02x400 = 0.16w (so a 0.25-0.5w resistor should be used)

            Comment

            • ajshoe
              ajshoe
              • Dec 2012
              • 477
              • usa

              #7
              Re: How to power backlit LED's?

              pics ??

              Comment

              • NeedsMoreFlux
                Senior Member
                • Oct 2017
                • 121
                • California

                #8
                Re: How to power backlit LED's?

                I am fixing a tv with led failure.

                When you turn on the tv it spikes to 30 volts / 8 LED's = 3.75V each!!!(Probably too high-manufacturer programmed this tv to burn them!) Then it drops to 18.5 volts = 2.3V each!!!

                I think your issue is that they are wired in series and ONE in the series failed!

                Scrape away a tiny spot on the solder mask on each side of each LED then use a digital multimeter in "Diode mode" If the meter doesn't light up the led-reverse the probes.

                I bet money you will find one bad one on each string. I bet these were given to you because they are bad!

                Don't destroy them-They could be worth ALOT of MONEY!!11!!1!!!1!1!!

                For 12 strips on this 60" vizio tv the sellers want $120-$240 for a set!!!!111!!1!!1!!!1!!11!!!!

                So, I bought 20 LED's off Ebay for $14!!! Aliexpress or digikey sell them cheaper if you can find a match!

                Let us know if you manage to fix them and sell them!
                Last edited by NeedsMoreFlux; 11-29-2017, 04:29 AM.
                Disclaimer: Don't trust a thing I say-I am frequently wrong!!!

                I have tons of spare parts, some used, some N.O.S. ham transistors and caps. Message me if you need any parts.

                Some of the things I've fixed:
                60" Vizio-bad LED's. iBook G4: Resoldered VCC Plug. Geo Tracker ECU: Swollen / Leaking capacitors. Windows Laptop: Soldered broken LVDS wires. Dryer: Burned contact on temp switch. Oven in R.V.: Bad contacts in relays-Exploded by the looks of them! Samsung Oven: Burned contacts on Relays. MSI Motherboard: BSOD-Swollen capacitors, bad graphics card, Moved SATA Input from SATA 1 to SATA 2 plug

                Comment

                • NeedsMoreFlux
                  Senior Member
                  • Oct 2017
                  • 121
                  • California

                  #9
                  Re: How to power backlit LED's?

                  $25 doll hairs per 2 strips!!! Check it out!

                  https://www.ebay.com/sch/i.html?_odk...0+led&_sacat=0
                  Disclaimer: Don't trust a thing I say-I am frequently wrong!!!

                  I have tons of spare parts, some used, some N.O.S. ham transistors and caps. Message me if you need any parts.

                  Some of the things I've fixed:
                  60" Vizio-bad LED's. iBook G4: Resoldered VCC Plug. Geo Tracker ECU: Swollen / Leaking capacitors. Windows Laptop: Soldered broken LVDS wires. Dryer: Burned contact on temp switch. Oven in R.V.: Bad contacts in relays-Exploded by the looks of them! Samsung Oven: Burned contacts on Relays. MSI Motherboard: BSOD-Swollen capacitors, bad graphics card, Moved SATA Input from SATA 1 to SATA 2 plug

                  Comment

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