Talk:Reducing power consumption of a raspberry Pi

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Re: Eliminating the 12V-5V converter in your low-power Raspberry Pi implementation

Dear BitWizard,

I have found your page most helpful in my own hack. I have duplicated your work and it works; Thank you!

I realized that VDD_BAT merely needs to be tied to 3.3V for it to work. There is no need to include a second 12V to 5V converter specifically for VDD_BAT. I have verified this with my setup and it led to further power saving (1.524W down to 1.44W at idle). Please consider trying it on your own Raspberry Pi too!

Regards, Ben

VDD_BAT is now tied to the +5V, right?

You need to know where the 5V goes to analyse what will stop working when you "lose" the 5V....

  • The CPU will work with a voltage from (I expect) 3.0V up to 5.5V. No problem. (most designs with this chip will tie it to the lipo battery voltage 3.2 to 4.2V, but raspberry pi ties it to 5V, and quotes an absolute maximum of 5.5V)
  • The 5V is used to create 3.3V through an LM1117-3.3 . This is no problem if you supply the 3.3V by other means. (The LM1117 will probably die if its input becomes significantly lower than its output, but we're planning on tying them together, so no problem).
  • 5V for the USB ports. If you don't have USB devices, or connect them through a powered hub this can be OK.
  • 5V for the HDMI port. I have a bunch VGA screens leftover, and little HDMI screens, so I have a few of those HDMI to VGA converters lying around. These use the 5V on the HDMI port and won't work off 3.3V. If you're not using a screen or using one with HDMI, no problem.

So... with two caveats, yes that's possible!