What's the design-spec power use on each voltage bus?


2 posts
by Sci » Tue Nov 06, 2012 4:04 pm
I'm working on a dedicated power & battery charging board for the Pi to make it more mobile. However I can't seem to find documentation on how much the 5v and 3.3v busses draw separately.
I know the 5v runs the 3.3v regulator, but if that regulator is fully utilised to it's datasheet's 800mA then it uses more power than provided by the 5v line. (EDIT: that's presuming the regulator is about 2/3rds efficient)

I'm aware I could go through the datasheet for each component and add up the peak current draws, or try to estimate it by running stress-tests while hooked up to independent bench supplies, but I though I'd ask first since if someone involved in the design reads this they'd surely have worked this out when planning out the power supply area. And it feels a little silly having to reverse-engineer what's supposed to be an open project.
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by Grumpy Mike » Sun Nov 11, 2012 8:41 pm
I know the 5v runs the 3.3v regulator, but if that regulator is fully utilised to it's datasheet's 800mA then it uses more power than provided by the 5v line..

So that tells you it doesn't.

The actual power draw depends on what the Pi is doing in respect to the video graphics chip and other such sub systems, therefore there is no simple answer.
With the Pi just showing the desktop I measure mine to draw 300mA. The Pi people specify 800mA just to be on the safe side when everything is running, in practice it will be less than that, but the exact value depends on what you have running.
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