Yes but remember the 3V3 is 'downstream' or in series with the 5V rail... so whatever current the 3V3 uses is already included in the 5V current measurement.mths. wrote:Hi klricks,
the RPi is powered by the microUSB socket. So, if I get anything right - there should be no problem with drawing 150 mA from 3v3 rail and 130 mA from 5v rail of a RPi B+ as long as the sum of total current used by the RPi and all periphery doesn't exceed the 2 A limit of the polyfuse?
Ok, it seems that I don't really got it right. If the current drawn out of 3V3 is included in the 5V measurement - why do I measure a higher current (150 mA) on 3V3 than on 5V (130 mA)?
Why can I measure 150 mA on 3V3 - without the RPi crashing or behaving strange - then?
Confusion is going on... :/
IIRC, what @cacti is referring to applies to A and B Pis, not the A+, (your) B+ and the P2B. Personally, since I usually need to use level-shifters for my application circuits, I tend to use (one of) such that has an on-board 5V to 3.3V regulator to provide an "external" 3.3V supply the current of which being drawn from the main 5V supply.cacti wrote:The 3v3 is produced by a dual switching regulator that can only deliver 50mA.
I don't have a comparable source in English at hand, but according to http://www.elektronik-kompendium.de/sit ... 910071.htm the current consumption of a RPi B+ powering 2 USB devices (keyboard and mouse), connected via HDMI, using ethernet and with a CPU-usage of 100% is about 500 mA (494 mA). So for my understanding there should be no damage done to the RPI B+ by drawing 150 mA (or even more) from the 3V3 power rail as there should be a lot of space up to the 1 A of the RT8020AGQW. Right?klricks wrote:According to this writeup the RPi VR is a 1A dual switcher: https://learn.adafruit.com/introducing- ... wer-supply
RT8020AGQW http://www.digikey.com/product-search/e ... 020AGQW-nd
What is unknown is how much of the 3V3 current is used by the RPi?