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Topic: Arduino pushes out power to VIN when connected to usb! (Read 502 times) previous topic - next topic

zubuyer

Hi There,

I'm working on a project where I've connected a buck converter to step down 12v to 7.2v to power my Nano through the VIN and GND pins. Now when I connect the USB to the Nano, the VIN starts outputting voltage and heats up the buck converter (mini360). I dont understand why this is happening. My Nano is also connected to a 16x2 Character LCD, which dims down when the buck converter is used while powered through the USB. Very confused here. Any explanation would be awesome!

Thank you in advance :)

raschemmel

#1
Jan 11, 2019, 12:13 pm Last Edit: Jan 11, 2019, 12:14 pm by raschemmel
Sounds like backfeeding through the internal protection diodes. Everything shares a conmon
GND right? Can you post a photo of a handdrawn schematic ? Have measures any voltages ?
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

zubuyer

Here I've disconnected everything. The USB is plugged in and it's showing 4.24v coming out of the VIN and GND. Happening to all my Nanos.

MarkT

Sounds like the buck converter is not able to handle backfeeding, add a schottky diode on its output.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

outsider

The 4.25V is sneaking backward thru the UA78M05 voltage regulator, that's normal. There's very little current, it has to flow thru several resistors and a diode.

zubuyer

Thank you for explaining. I'm just worried if the buck is going to get too hot. This one time, it got so hot I was unable to hold it. Is there a way to avoid this? As MarkT said, I tried putting a schottky diode in serial with the VIN and GND, now the diode is getting too hot. Any ideas?

Paul__B

I'm working on a project where I've connected a buck converter to step down 12v to 7.2v to power my Nano through the VIN and GND pins.
And there is a big mistake.

If you have a proper regulated supply - as distinct from the essentially useless one on the UNO/ Mega/ Nano/ Pro Mini - then you set it to 5 V and use it to power the 5 V pin.

However that is clearly not your problem just for the moment.  If you are powering the buck converter, then as it is, you are feeding 7.2 V into the on-board regulator, you cannot "back-feed" it with 4.24 V.  If you are not powering it then there is some vague possibility that back-feeding it at 4.24 V might do something.

Your description makes no sense.  Also
I tried putting a Schottky diode in serial with the VIN and GND, now the diode is getting too hot.
"in serial with the VIN and GND" makes no sense either.

You are doing something wrong.  It is not "back-feeding", you are making a wrong connection somewhere.  If you can figure out what, or provide enough information (photos) so that we can spot it, then it can be corrected and you can re-calibrate your buck converter to 5 V and feed it in to the "5V" pin.

zubuyer

Thank you for your response Paul__B,

I am simply using a mini360 buck to regulate the 12v input to 7.2v output to power the Nano. I hooked up the out + and - to the VIN and GND on the Nano. Everything works great when I use the external (12v) power supply. But while the 12v is connected, if I put in the USB to program the Nano, it back feeds 4.25v out to the buck. This is the part that I'm having trouble with. I'll be using a 3S 11.1v Lithium Ion battery pack to power my device and I rather make it as safe as possible. Any suggestion would be great.

I attached the schematic with this post. Please see.

outsider

Try putting a 1k resistor as a load from VIN to GND, see if it helps (or makes a difference).


Wawa

Now when I connect the USB to the Nano, the VIN starts outputting voltage and heats up the buck converter (mini360).
The buck should not heat up when <=5volt is connected to it's output,
but it could if a load is connected to it's input (back-powering through the buck).
So is there something connected to the 12volt input of the buck when this is happening.

I would trim the buck to 5volt, and connect it directly to the 5volt pin.
The Nano has a USB backflow protection diode, so no danger if the Nano is powered both ways.
Leo..

Paul__B

The buck should not heat up when <=5volt is connected to it's output,
As I said back in #6, but the OP's description is incomplete or confused.  Can't do anything else at this point ...  :smiley-roll:

TomGeorge

Hi,
Can you post a picture of your project connected in the fault mode?
What is the 12V supply that you are using?

Thanks.. Tom.. :)
Everything runs on smoke, let the smoke out, it stops running....

zubuyer

@Wawa: Yes there is. I think I should have included the whole diagram. I'm using the same 12v supply to power the Nano through a Buck and power the A4988 driver to drive a Nema17 stepper motor. Please see the complete diagram attached.

sorry for the terrible image quality.

Wawa

Add a small diode (1N4004, 1N5819) between +12volt supply and buck +input.
That should stop backpowering the motor driver through the Nano's regulator and the buck converter.
Leo..

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