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Power Available to HAT

Wed Feb 11, 2015 5:56 pm

Hi i want to design a HAT but havent been able to find out how much power i can take from the 3.3v line. Also is the 5v line straight from the USB or is it fused / limited?

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Re: Power Available to HAT

Fri Feb 13, 2015 12:38 pm

Is there no information on the B+ / B2 3V3 switcher?

Hope someone can help me out?

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Re: Power Available to HAT

Sun Feb 15, 2015 7:47 pm

Not what you asked, but mentioning it for comparison; for the Pi Model A and B "The maximum permitted current draw from the 3.3 V pins is 50 mA." source:

For the A+, B+ and 2B, things are *much* better than before. Adafruit has an article on it: ... wer-supply

The 5V0 from the pins still bypasses the fuses (if I understood correctly).
Microcontroller addon boards and software for Raspberry Pi A+/B+/Pi2:
- ARMinARM: ARM Cortex-M3 (STM32)
- AVRPi: ATmega32U4 & ATmega328 ("Arduino")

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Re: Power Available to HAT

Mon Feb 16, 2015 11:34 am

The 5v pins on the GPIO header are after the polyfuse and the "ideal diode", so limited to what those will pass.
If powering the Pi from the HAT, there's no protection, other than the over-voltage diode

I've not found any details about the 3v3 supply, other than the cryptic label "2A" next to L1 on the B plus diagram. That possibly means that it won't saturate below 2A, but doesn't give any clue about how much current we can source

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