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I have developed couple of hats having own micros. In the prototypes I was taking power from the 3.3V RPi. I know that it is not recommended, so I have added own LDO connected to the 5V pin. Strange things started to happen (random resets of my micro). I had to add 10u electrolytic capacitor on the LDO input (there is another 1u as DS advises) to stop this to happen. Is the voltage on 5V pin as bad as it looks like? Maybe it is only my RPi.

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The 5V power rail is driven directly from the micro USB socket (power supply), i.e. it is unregulated. Its quality depends on the quality of your 5V power supply.

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"I know that it is not recommended" - why do you think this?

The 3.3V pin is there for PRECISELY this reason, and can supply up to 800mA.

The Pi actually has an on board regulator which will perform better (and more efficiently) than any linear regulator you can add.

See Raspberry Pi Power Limitations

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  • As fasr as I know there is a 50mA limit for the hat. My hat thwrically can draw up to 160mA if the user adds power consuming elements for example LEDs. I will ask RPi foundation to clarify it – P__J__ Oct 27 '17 at 1:43
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    @PeterJ_01 This is one of the MOST pervasive Pi MYTHS. The original Pi had a linear regulator, which was designed to provide 51mA. If you actually read the link you will find links to actual test results. All Pi with a 40 pin header have switch mode regulators. – Milliways Oct 27 '17 at 2:38
  • It is a very good news for me :). Formally I need to check - because otherwise the Foundation will not let me use the term "hat". Yes you are 100% right it has vanished from the hat requirements (but I am sure that it was there some time ago) github.com/raspberrypi/hats – P__J__ Oct 27 '17 at 8:48

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