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Topic: Mega2560 board, IC7 gets very hot? (Read 2 times) previous topic - next topic

SurferTim


The Mega2560 has problems when powered by the Vin (barrel jack) and the usb simultaneously. If you had your Mega connected to usb and external power applied to Vin, it could have damaged the board.

I usually don't quote myself, but I do not see this as "WARNING DANGER DANGER". I always like your input tho. Sometimes in my haste, I forget a detail that could be important.

retrolefty



The Mega2560 has problems when powered by the Vin (barrel jack) and the usb simultaneously. If you had your Mega connected to usb and external power applied to Vin, it could have damaged the board.

I usually don't quote myself, but I do not see this as "WARNING DANGER DANGER". I always like your input tho. Sometimes in my haste, I forget a detail that could be important.



Yes I do go over the top sometimes, I'm sorry, but it's not my fault really, I just sometimes frizzle at the warnings and cautions given out to beginners here sometimes that are not fact based. They have enough on their plates as it is learning to use their arduino board properly and learning the electronics they need to so as to not cause self inflicted damage.

I have no negative issues with you, just with the statement you made this one time.  ;)

Lefty

SurferTim

@retrolefty: Now that I seem to have your attention on this, do you see a problem with IC7 if Vin > 10v? That would effectively overdrive the Vin input to IC7, would it not? Could that cause a latchup condition on the output?

Just trying to figure out why it gets hot.

retrolefty


@retrolefty: Now that I seem to have your attention on this, do you see a problem with IC7 if Vin > 10v? That would effectively overdrive the Vin input to IC7, would it not? Could that cause a latchup condition on the output?

Just trying to figure out why it gets hot.



The op-amp input pin is wired to a voltage divider the cuts Vin in half to the pin. I don't know what the input pin voltage limit is for that specific op-amp, anyone have a datasheet link to it? But as the Vin limits are rated as:
Quote
Input Voltage (limits)   6-20V

That means the input pin of the op-amp is designed to work at up to 10v which is well above the Vcc the op-amp is powered by, so obviously the op-amp is designed to handle input pin voltage higher then it's running Vcc is. Again a datasheet is needed to see what the true voltage limit for the op-amp is. I think the op-amp specification we need to know is called it's input common mode rejection voltage rating?

Lefty

SurferTim

#9
Dec 05, 2012, 09:22 pm Last Edit: Dec 05, 2012, 09:56 pm by SurferTim Reason: 1
Datasheet.
http://www.ti.com/lit/ds/symlink/lmv358.pdf
Max voltage any input = 5.5v
That means 11v is the upper limit to Vin without overdriving the op-amp. :(

edit: Seems like you could fix that with one well-placed zener diode.  ;)

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