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Topic: External supply at 5v pin (Read 2 times) previous topic - next topic

Tilemachos

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Vs the older definition the arduino folks used in their older boards:

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5V. The regulated power supply used to power the microcontroller and other components on the board. This can come either from VIN via an on-board regulator, or be supplied by USB or another regulated 5V supply.

I'm aware of no official reason given for their change of recommendation on the use of the 5V pin.

Lefty


Thanks Lefty! I didn't know that. That's really odd!

Tilemachos


Tilemachos, I don't know what your plan is with the zener, but it doesn't sound good.
If you need more power, use a good power supply with a good +5V. The Uno board is designed to be able to get power via the +5V pin (but only if it is +5V and not higher).


Well, I don't need more power, just power up Arduino from 4xAAA rechargeable batteries, 4x1,2V=4,8V, which voltage can't enable regulator.

retrolefty


retrolefty, so the text has been changed.

I thought it was only with the Mega a problem but not with the Uno.
The warning can be read in different ways. Perhaps they ment to say that without using the voltage regulator the board is 'unprotected' against higher voltages. And there are many cheap adapters that supply more than 5V.

No their recommendation on the older boards was it was OK to use a regulated 5vdc power supply to the 5V pin, the newer recommendation is to not try and power the board via the 5V pin. There must have been a reason for them to update the pin 5V recommendation, we just don't know the reason why.
Lefty


Tilemachos, I don't know what your plan is with the zener, but it doesn't sound good.
If you need more power, use a good power supply with a good +5V. The Uno board is designed to be able to get power via the +5V pin (but only if it is +5V and not higher).

CrossRoads

The reason was discussed a while ago. The 1117 5V regulator is susceptibe to damage when reverse driven. The earlier posts discussed bricked boards after putting 5V into the board via the header pin. A member of the team discussed it with us.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
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Tilemachos


The 1117 5V regulator is susceptibe to damage when reverse driven. The earlier posts discussed bricked boards after putting 5V into the board via the header pin. A member of the team discussed it with us.


Thanks CrossRoads.
Is there a solution about this? Sure, I can regulate the external voltage, but how can I protect the regulator?

When I plug in only the usb, there is no reverse current in the regulator?

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