Arduino Forum

Using Arduino => General Electronics => Topic started by: golf_bht on Jun 18, 2012, 07:11 pm

Title: MOSFET Help needed
Post by: golf_bht on Jun 18, 2012, 07:11 pm
I am trying to do PWM for motor. I was trying to hook the pwm pin to mosfet but it won't work.
the mosfet i am using is p55nf06. the voltage for the motor is rated at 36V 3.5A

the led hooked to the arduino out put seem to work fine, but the mosfet did not turn on.

What else do I need to make it works. Do I have a dead mosfet?

I wire the arduino output to pin 1 on the mosfet. What have i done wrong?
Title: Re: MOSFET Help needed
Post by: majenko on Jun 18, 2012, 07:25 pm
You either have a dead MOSFET, or you have connected it up wrong.

Without you telling us how you connected it up, it is impossible to say which.
Title: Re: MOSFET Help needed
Post by: kivig on Jun 18, 2012, 07:34 pm
It may be important which side do you connect MOSFET to. High-side +/motor or low-side GND/motor. Had to do this only once, but if I remember right N-channel should be low side. But that's definitely not the way it should be explained :)
Of course, as majenko said it's hard to tell without details
Title: Re: MOSFET Help needed
Post by: Magician on Jun 18, 2012, 10:14 pm
Have you connected ground arduino and external 36V PSU?
Other things,
Quote
VGS(th) Gate threshold voltage
for this transistor 3-4 V , may be too high. Look for logic level MOSFET, or select the lowest value if you have a few transistors.  Gate threshold voltage chart shows nice rise up above 5V, so there is a good chance you''ll find one, if your arduino isn't 3.3V version ?

Title: Re: MOSFET Help needed
Post by: MarkT on Jun 19, 2012, 03:29 pm
Its simple, its not a logic-level MOSFET and needs 10V of gate drive - you give it 5V and not much will happen (perhaps a few tens or hundreds of milliamps might flow, depending on temperature and the specific device.

The threshold voltage is not the spec to look at for a switching application (basically ignore it).  The specification that matters is the "Rds(on) at Vgs=...." one.   This tells you the resistance when the device is on, and the gate-source voltage difference required to guarantee this for all operating temperatures and devices.  You should provide at least that voltage to switch the device on.

So a typical logic-level MOSFET will say something like "Rds(on) at Vgs=4.5V :  0.01 ohms"

The threshold voltage (which varies a lot between devices and changes a bit with temperature and age) is the voltage below which the device switches fully OFF.  For all switching applications we make Vgs=0V for off, so this spec doesn't matter.
Title: Re: MOSFET Help needed
Post by: golf_bht on Jun 19, 2012, 04:36 pm
Thank a lot for all reply. Coming from media art background, i know nearly nothing about electrical engineering.
With that said... What other component is needed to successfully drive the mosfet @36V/5A PWM

How do I safely reduce the voltage of 36V battery to 5 V for the arduino board.

once again.... thank you very much for your help :)
Title: Re: MOSFET Help needed
Post by: Docedison on Jun 19, 2012, 06:44 pm
Use a switching type regulator. 36V in switchers @10A or better are available on Ebay for about $7-10 from several Mfrs they are standard PSU's for large Industrial Computer main frame PSU's as local board level power supplies/converters and are available as NOS from several stores. These parts are used because it is easier to develop high current local sources (switchers) than it is to make one big 5V 50 A supply and then have to deal with the voltage losses that would be incurred in trying to distribute the 5V power. The same thing is done on all new PC mother boards for the 1 -2.5V power supplies for the Microprocessor as the IR losses would be too great if they were part of the main PSU.

Doc
Title: Re: MOSFET Help needed
Post by: golf_bht on Jun 20, 2012, 06:00 am
What other component do I need to drive the gate of this mosfet form the logic level arduino
Title: Re: MOSFET Help needed
Post by: majenko on Jun 20, 2012, 09:55 am
You could use a BJT to switch the gate with a higher voltage...
Title: Re: MOSFET Help needed
Post by: Magician on Jun 20, 2012, 01:49 pm
Quote
i know nearly nothing about electrical engineering.
I'd not start to learn designing 150W driver.  May be it's just me. There is a link to shield, you can buy or replicate using posted diagram:
http://www.emartee.com/product/41874/Arduino-4-Route-MOSFET-Button-IRF540 (http://www.emartee.com/product/41874/Arduino-4-Route-MOSFET-Button-IRF540)
http://www.emartee.com/product/42040/Arduino%204%20Route%20MOSFET%20Button%20IRF540%20V2.0 (http://www.emartee.com/product/42040/Arduino%204%20Route%20MOSFET%20Button%20IRF540%20V2.0)