Fan switch on/of and speed regulation - LCD Repair from overheat defect

Hi, some week ago with the arrival of summer heat, I had an overheating problem of the LCD monitor. The problem and solve is show into video that you can see at the and of this post.

Here I want report the simple electronic circuit to make an on/off with speed regulation. All with only a 1 mosfet transistor :)

The mosfet you can see below, is taken from old xbox360 motherboard, is N channel, I check it on datasheet.

I have looted many mosfet from that xbox :D

Tipicaly most mosfet has 2~2,5V polarizing tension. You first try to polarizing using this tension and see how it works. I using 10Kohm resistance between Gate (RB) and GND and after calculate the other. Below the schema.

In this case, I have a control signal of 5V and use another 10Kohm resistor, to have 2,5V on G mosfet pin. With this configutation I see that it not working at full speed, the fan speed is high but not at full speed.

For me is still too fast, I add a 1Kohm trimmer and 47Kohm 1/2W of RL. In this way I speed down. Now the fan have the right speed .. for me ;)  and with the trimmer I also have some speed ajustament.

In this example the mosfet works as current regolator, not as switch. I add RL to help him to working at low temp.

after all this job .. my monitor go back to works fine from 2~3 weeks :)

 watch the video of the defect and how I make this repair ;)