Re: [PLUG] Old Raspberry Pi Max Input Supply Voltage

[Steve Litt via plug <plug@lists.phillylinux.org>]

As far as I know, if the Pi doesn't draw much current, you can use a
TO220 package 7805 to regulate to 5 volts.

https://en.wikipedia.org/wiki/78xx

I think you'd need to use a higher input voltage to the 7805 than 7
volts. Probably 8 volts. You should probably mount the 7805 to a small
heat sink.

SteveT



Rich Mingin \(PLUG\) via plug said on Sat, 9 Dec 2023 17:40:20 -0500

>If you put 7V into the GPIO inputs, you will have a warm Pi for a few
>hundredths of a second, and then no Raspberry Pi at all. The GPIO
>power inputs are *not* regulated and are *very* sensitive, they want
>5V input. Not 7V, not 5.5V, not even 5.1V. I popped the VRMs on a lot
>of early Pis by powering them via GPIO.
>
>I *think* cooking the inputs via GPIO will also perma-brick the Pi,
>since you'd be killing components further inboard than the usual
>micro-USB input, which feeds a regulator, which then feeds into where
>the GPIO pins tie in.
>
>I looked for some documentation to support, and the only things I
>found said to supply 5V to GPIO, never more, and design your power
>hats to fail *low*, since failing high will cause board death. Sorry I
>don't have more supporting information to cite.
>
>On Sat, Dec 9, 2023 at 5:32 PM Casey Bralla via plug
><plug@lists.phillylinux.org> wrote:
>>
>> I've got an _OLD_ Model A Raspberry PI (the second model produced,
>> which was a cost-down version of the first Model B).
>>
>> I'm using a 3" NTSC video display board with it that accepts the old
>> composite video, but I've got a power problem.
>>
>> The video display requires 6-12 volts, but the PI asks for 5 +/-
>> .25V. I've run this combo using 2 wall warts, but I'd much rather
>> use a single supply.  My thought was to power the old PI via the
>> GPIO pins with a single 7-volt wall wart I've got lying around.
>>
>> Do you think this would fry the Pi?  I expect that it will only make
>> the Pi run a little warmer than normal, but would appreciate some
>> electrical engineering advice here.
>>
>> TIA!
>>
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