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Topic: MOSFET N & P and relay (Read 2 times) previous topic - next topic


Mar 23, 2011, 11:03 am Last Edit: Mar 23, 2011, 11:35 am by yopaii Reason: 1
HI everyOne,
Here is what i am doing, and..what is going wrong ..
I use a N channel Mosfet and a P Channel to switch on and off the motor of an electric screw driver.
I think there is a little problem in my schematic because when the pin of the ARDUINO is LOW, i still have 8,6 V on the Drain of the P channel Mosfet
When the PIN is HIGH, I have 10 V on the Drain, and the relay is working good and the motor is turning.
When the PIN is LOW, the relay and motor don't work, perfect ... but i still have something like 8.6 V on the DRAIN.
is it normal ?
Do i have to do something to avoid this ?
If i plug a 10mm led in place of the RELAY & MOTOR, with a 390 Ohm resistor to the ground, i can see a little activity on the LED ... the 8.6V.
PIN HIGH of the ARDUINO and the LED is fully On ..
Thank you for your advice ...

Terry King

Maybe the 10K pullup on the PFET is'nt enough to keep it cut off..  try 1k .  Maybe leakage in the NFET?

What's the voltage on the PFET gate compared to it's Source??
Regards, Terry King  ..On the Red Sea at KAUST.edu.sa
terry@yourduino.com  LEARN! DO! (Arduino Boards, Sensors, Parts @ http://yourduino.com


Out of curiosity, if you are driving a relay from the Arduino, why don't you just use a single bipolar resistor?
My New Arduino Book: http://www.arduinobook.com


Yes, why the high-side switch, that makes things much harder and doubles the components

Rob Gray aka the GRAYnomad www.robgray.com


Ohh ... that's right ... I already had this circuit with mosfet and i tried to use it with my new setup.
the thing is, the electric screwDriver is for away (15 meters) from the Arduino.

Arduino > Mosfets    >>>>>>>>>>> 15 meters >>>>>>>>>>> relay + screwDriver Motor

You're probably right, i should be able to do it simpler.

If i follow this schematic
Arduino > pinout >>>>>>>>>>>> 15 meters >>>>>>>>>>> relay + screwDriver Motor
I will probably loose a lot of signal to trig the relay no ? that's way i wanted to use a 10V signal instead of the 5V outputPin

Any advice on which component i should use ?

thank you

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