Raspberry Power DC Power Supply

Having done some further investigation I have decided that a 5v DC PSU would be the best approach. This would reduce the complexity, cost, and inhibit any of the potential overheat scenarios.

The output connector on the model that Problemchild referenced earlier has output connector dimensions of: 2.1mm x 5.5mm x 12mm.

Is this size suitable, or is there a more recommended/common connector size?

Hi Paul,

I feel the 2.1mm connector is the most common one, yes. There are also connectors with the same external diameter but with 2.5mm internal diameter.

There is a DC connector available that will accept both sizes, but that's possibly overkill. Anyway, the same PCB footprint usually works for the 2.1mm and 2.5mm connectors

(i.e. a footprint like the one below).

Thanks shabaz. Is that eagle you're using there?

Hi Paul,

It is, I think a similar package may already be in a supplied library, I tend to make my own off the part datasheet, so I just pasted a screenshot of it.

The problem with those 5.5/2.1mm connectors is that they are common. People will have physically compatible powersupplies lying around the house that are of a different voltage, usually 12V or more. This will fry your 'pi for sure.

That's true, if Paul wants to design for minimum user error risk, then a different connector or diameter may be an option. There are other non-technical ideas like the BBB and RIoTBoard use, where they have a big label marked 5V on the connector. I think it does work as a good reminder, a nice non-technical solution.

I guess it really depends on your requirements Paul, and who will use the adapter (e.g. experienced users will already label their supplies or double-check before plugging in, but a kid might not). I have 5, 9, 12, 15, 24, 48V supplies all with this connector so I need to take care extra as an example, so I triple-check : )

Thanks Rew and shabaz. Good feedback.

One of the earlier suggestions about using a 5v PSU directly indicated that many people have them lying around, so I thought I'd play on that strength, which is where the readily accessible standard connector may be an advantage.

If over-voltage (which is very likely to present an issue) needs to be mitigated, how about placing a resettable fuse in series with the +5 line and then installing a zener diode (maybe 2 or 3 in parallel) that breaks down on a reverse voltage of over 5.3v for example. Would this trip the resettable fuse?

Resettable Fuse:

http://uk.farnell.com/bourns/rm008-240-2/fuse-resettable-ptc-240vac-80ma/dp/2366925

Example Diodes:

http://uk.farnell.com/nxp/plva653a-215/zener-diode-0-25w-5-3v-sot-23/dp/2439627?ost=zener&categoryId=700000004649

http://uk.farnell.com/rohm/kdztr5-1b/diode-zener-5-1v-1w-sod-123/dp/2143976

Hi Paul,

You could use such an approach based on zeners as you say.

I think just a text label could be "good enough" for RPI protection maybe (not everything needs an electronic solution), but a zener/fuse option may be cheap enough too (the zener

needs to handle a high amount of current for a length of time, otherwise it could be damaged too - there are other tricks that use zener + MOSFET as an example).

There are even dedicated ICs for this situation too - that's possibly a bit 'over the top' for protecting an RPI though.

Hi Paul,

You could use such an approach based on zeners as you say.

I think just a text label could be "good enough" for RPI protection maybe (not everything needs an electronic solution), but a zener/fuse option may be cheap enough too (the zener

needs to handle a high amount of current for a length of time, otherwise it could be damaged too - there are other tricks that use zener + MOSFET as an example).

There are even dedicated ICs for this situation too - that's possibly a bit 'over the top' for protecting an RPI though.