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Resistor Pixel?

Discussion in '101 Display Basics' started by tooms, Sep 30, 2019.

  1. tooms

    tooms Full Time Elf

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  2. scamper

    scamper Dedicated Elf

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    All leds run on low voltage typically around 2v depending on colour.
    When you run 12v strings, you must get rid of all that extra voltage, so there are 2 ways to do this, by using a dropping resistor, which is inefficient and causes a fair bit of heat or a regulator, which is more efficient and still causes heat, but not as much.
    regulator ones are generally the better option but you obviously pay a little more.
    The voltage drop has been the big controversy in led strings for ages when comparing 5v vs 12v. (obviously you need to drop less voltage in 5v so draw less current)
     
  3. AAH

    AAH I love blinky lights :) Community Project Designer

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    The heat will be identical between the 2 with a very slight possibility that the regulator style will actually run ever so marginally hotter as you still have to drop the same amount of volts at the same current so for a linear regulator there's no power benefit. The regulator itself will use a small amount of current to run. Not knowing what reg that they use this could be from microamps to a milliamp or 2.
    As far as I know the reason for resistor or regulator is to reduce the heat in the 2811 pixel chip as the resistor style effectively dumps current into a shunt regulator or possibly even just a zener diode within the pixel chip to provide its 5V reference voltage. Having the regulator separate to the pixel chip means that the heat is going into the regulator chip and not the pixel chip which already has to handle dumping the excess heat as it regulates the 18.5mA per colour.

    The shortest version of this story is that this is yet another reason for 5V pixels over 12V ones. The 12V ones have to drop about 9-10V as waste heat purely so that people don't have to be as critical about supplying a nice stable 5V.
     
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