HDMI current booster fixes Raspberry Pi video instability

Orlando Cosimo with Creativity/Design blog was experiencing instability problems with the HDMI output on the Raspberry Pi which are typical when using an HDMI to VGA adapter. He devised this solution using three resistors and an LM317 voltage regulator. Orlando states, “This addon hardware extends a past project and it allow to increase the flow current on HDMI port. No other configurations are necessary and it solves definitely every problem on HDMI port for every revision of Raspberry Pi.”

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  1. “fix” make no sense, an LM317 has a drop out of atleast 1V even at very low currents, (plus ~1.2V over the sense resistors when used as a current source). I cannot possible add any current since it is parallel with a diode that drops less than 0.8V

    1. I first thought this was a booster that would increase the vcc pin’s current, but it’s actually more like an external power supply for this pin. In that way the fix makes sense but I wouldn’t call it a current booster but more like an external current adapter.

      1. No, it doesn’t. Look at the guy’s schematic: the whole thing he added is shorted by the diode D1, so it has absolutely no effect.

  2. The diode is part of the Pi, the LM317 is connected to the device side. This diode prevents current from the LM317 from flowing into the Pi. The LM317 is set up as a current (not voltage) regulator, it’s forcing current into the +5V lead of the attached display.

    1. but the input to the LM317 is shown as 5V, so the output will never be anymore than 4V.
      The out from the diode is the same 5V minus the max 0.8V drop = 4.2V, the LM317 doesn’t do anything.

  3. From the description of the problem, the 5V source on the Pi can’t provide enough current, which means the voltage will drop below what the LM317 is providing, therefore the LM317 will provide the current to the HDMI device.

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