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Topic: Need some help with MOSFET (Read 1 time) previous topic - next topic

Hi!

For my project I want to remotely shutdown my application. For this I though of a circuit using a power n mosfet:

- I use an IRF510 MOSFET
- GND from the Arduino is connected to the drain of the mosfet.
- GND from the power source (12 V adapter) is connected to the source of the mosfet.
- The gate is connected with a digital port.
- There is a switch connected both to the drain and source to enable the application (to give the application some time to set the gate)

Now I have some problems with the gate. First I connected the gate and source with an 100k resistor to keep the gate low. But then when I set the digital port to LOW it still gave power to the Arduino. I found on this forum and on some other sites that I could try to connect the gate with the GND from the Arduino (using an 100k resistor). But even with this change I cannot disable the mosfet from giving power to my Arduino.

Any thoughts? Thanks in advance!

retrolefty

First of all a IRF510 will not operate properly with an arduino output pin because it is NOT a logic level mosfet. A logic level mosfet gate can be fully turned on with +5vdc, a non logic level mosfet requires => +10vdc to full turn on.

As far as your failure to turn off, I would want to see a wiring drawing of how you actually have things wired up before guessing. First impression is that 100K ohms is awful large to try and discharge the gate capacitance.


Lefty

I am not very good at this but here is a schematic:



The ground on the left is the ground of the Arduino. I did not display the switch, that is just a connection that bypasses the MOSFET.


My first thought was that the MOSFET was not correct, would it be possible using this MOSFET? I do not have an alternative at this moment.

CrossRoads

For cutting off power, you really need something like these

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=869-1053-ND
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=MTP50P03HDLGOS-ND

Very low Rds so you're not dropping a lot voltage across the MOSFET when it is turned on

With N-Channel part, you really want to use it to open the ground circuit.
And as GM says, IRF510 needs 10V to get its low Rds of 0.54 ohm (540mOhM)
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Would I be able to use an n-MOSFET? Then I have to do less modifications.

Coding Badly


retrolefty



commanda


First of all a IRF510 will not operate properly with an arduino output pin because it is NOT a logic level mosfet. A logic level mosfet gate can be fully turned on with +5vdc, a non logic level mosfet requires => +10vdc to full turn on.

As far as your failure to turn off, I would want to see a wiring drawing of how you actually have things wired up before guessing. First impression is that 100K ohms is awful large to try and discharge the gate capacitance.


Lefty



If I'm understanding correctly, what you're trying to do is power off the Arduino, sending a control signal from the Arduino itself.
This will not work with an N-channel fet.  The Arduino ground is connected to the mosfet drain.  The Arduino output pin, when set to low, only goes to its own ground. So the mosfet gate is still at the same potential as the drain.

A P-channel mosfet in the positive supply line might work.

A better approach would be to investigate the sleep library.

Amanda

CrossRoads

GM, yeah had Mike on the brain from another post ...
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

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