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led 3w power supply ?

Discussion in 'Power Electronics' started by mark krawczuk, Nov 7, 2019 at 4:10 AM.

  1. mark krawczuk

    mark krawczuk

    Dec 17, 2015
    i have some 3w star type leds, 700 ma, f.v 1.4 to 1.8v.
    i need to run 8 of these from a 12.8v ( auto battery) power supply.
    what would be the best way to connect these up ? in series or parallel ?
    how much total current will it need ?
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    LEDs are not operated directly in parallel. If in parallel, a means of distributing the current equally is needed.
    To operate them in series, you'll require 8×1.4 V to 9×1.8 V (11.2 V to 14.4 V). A 12 V power supply can barely supply the LEDs at the lower end but not if the pass voltage is at the higher end.
    I suggest a mixture of parallel and series mounting: 2 parallel strings of 4 LEDs in series each. Plus you'll need a means to limit the current - LEDs cannot be connected directly to a vooltage source.
    I recommend you read our resource on the topic.
  3. bertus



    Have a look at a dedicated led driver like the LM3421.


    Attached Files:

  4. jaksonlee


    These power LED stars offer an extremely high light output in an energy efficient way. The power LED comes mounted on to special PCB star that acts to draw heat away from the LED, therefore extending its operational life. This makes them perfect for many lighting applications and this sheet explains how.
    The LED is a 3W LED and the forward voltage is rated at 3.5V to 4.0V so for the purpose of the calculations a forward voltage of 3.7V is used. The typical current of the LED will therefore be 810mA (from Power = Current x Voltage). The power source used with the LED must therefore be able to deliver at least 810mA. Since most power supplies will be higher than 3.7V a current limit resistor will be required. The next page shows an example of using this LED with a 5V power supply. The resistor also needs to handle 810mA flowing through it and as a result will need to be a power resistor. Please note that during use both the star LED and the resistor will get hot and shouldn't be touched.
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