Using Ardunio and MOSFET to drive 5V to 12V

[focspike]

Hello,

I am working on a project which involves using an Arduino Mega, and I am trying to use an NMOSFET (BUZ101S) and an NPN BJT(2N3904) to drive the 5V output from the MCU back and forth between 0V and 12V across "SOL".

At the moment, the problem I have is that Vgs always stays high, thus driving SOL on all the time, and I cant figure out why this occurs.

Here is my circuit diagram:

https://i.imgur.com/ls9l9oa.jpg


Any help is appreciated. Thanks!

 

[MrAl]

Hi,

You need to connect your MOSFET to the bottom of SOL, not the top. The MOSFET does not turn on well when the source connects to the load like that. Connect the drain to the bottom of the load (SOL) and the source to ground and top of SOL to +12v and it should work ok.
Also, you dont need a resistor as low as 300 ohms to drive the base. 1k or even higher should work.

 

[focspike]

I was unable to make it work by switching around the MOSFET and SOL.

Does the 300 Ohm resistor play an integral part in why this circuit might not work?

 

[focspike]

I want to also note that from the advice from some others I am using a diagram almost identical to this, with the exception of removing the 4N35 in place of my NPN BJT

http://forum.allaboutcircuits.com/attachment.php?attachmentid=68823&d=1400757981

 

[MrAl]

Hi,

The best way to connect it is the way i told you. If it does not work, then something simpler is wrong like a blown part or something. it could be that the transistor is burnt out now.

A 1k resistor from the Arduino to the transistor should be a good value. That will allow the transistor to turn on properly.

I almost forgot to ask, what does "SOL" stand for, is that a solenoid?