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Topic: Driving Mega2560 from external 5V bricks USB port (Read 10 times) previous topic - next topic

SurferTim

Thanks for that info. I thought T2 may be the culprit back in reply #5.

kurt6string

#21
Apr 07, 2012, 02:12 pm Last Edit: Apr 07, 2012, 02:15 pm by kurt6string Reason: 1
I'm not sure it's the culprit, but removing it prevents using both power supplies simultaneously while allowing usb communications. What do you think T2 might be doing to damage the 16u2?

SurferTim

#22
Apr 07, 2012, 02:19 pm Last Edit: Apr 07, 2012, 02:25 pm by SurferTim Reason: 1
It was just a suspicion. You should know soon. How long would they last with T2 on the board?

edit: I don't know, but the gate on it is only disabled (gate high) by the voltage on Vin being higher than 6.6vdc. If you power the device with +5v, the gate is left low, which enables the fet T2. They don't do a great job conduction reversed, but they do.


kurt6string

I'd say the boards died within a 2-3 day time frame. I can't pin it down any closer than that because the usb cable was only plugged in intermittently but if I had to guess I'd say they had maybe 4-5 hours of time plugged into both usb and external power.

SurferTim

@kurt6string: Keep me posted on the results of your test. I have a project I put on hold until this is resolved.

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