How to get power from USB and/or Voltage regulator ?

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#1
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Hey everyone,

I'm trying to design a development board.
I want it to be powered from USB or an external dc source which will be regulated on the board.

I would like to join both USB and the regulator to one 5v bus. At first I though of using schottky diodes between the supplies and the 5v bus. But this way I loose regulation.

Is there anyway to have both supplies supplying the 5v bus ?

If not, is there any way to showdown the regulator if usb voltage is present ?

I only have access to jellybean components (eBay mostly).

Thanks in advance,
Mike.

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Dual Ideal Diode is exactly what you need. Replace "wall adapter" with your voltage regulator, and "battery" with your USB power rail.

Warning: Grumpy Old Chuff. Reading this post may severely damage your mental health.

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I would recommend reading this:

http://www.ti.com/lit/an/slyt118...

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Thanks for the info, the in rush current limit was new to me.

That ideal diode ic sounds awesome, too bad it's not common enough to be on eBay, so I can't really get it.

Any other alternative ?

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The 5V of USB can be quite low, as low as 4.40V. With a diode, that would be around 4V.

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Quote:

That ideal diode ic sounds awesome, too bad it's not common enough to be on eBay, so I can't really get it.

What is the reason you are restricting yourself to EBay? E.g. DigiKey ships to Israel: http://www.digikey.co.il/product...

(My apologies if you are within the borders of Israel but do not speak/read Hebrew)

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Yeah I know that digikey shipps here, but the shipping costs almost 40$.

So it's not really viable for small quantities.
And this will probably be a one off board.

Than again, I could get it form RS (https://il.rsdelivers.com)
Though they are kind of expensive, but shipping is only 9$.

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If you go to the product page at Linear Tech you will fintt that there is a link to get samples. I do not know at all about Linears sample policy, but it might be worth a look/try..

As of January 15, 2018, Site fix-up work has begun! Now do your part and report any bugs or deficiencies here

No guarantees, but if we don't report problems they won't get much of  a chance to be fixed! Details/discussions at link given just above.

 

"Some questions have no answers."[C Baird] "There comes a point where the spoon-feeding has to stop and the independent thinking has to start." [C Lawson] "There are always ways to disagree, without being disagreeable."[E Weddington] "Words represent concepts. Use the wrong words, communicate the wrong concept." [J Morin] "Persistence only goes so far if you set yourself up for failure." [Kartman]

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But even with a ideal diode, the USB minimum voltage of 4.4V can be a problem.

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Oh well, since it's a development board after all I think I'll just use a jumper to set the input.

Thanks anyways guys.