Newbie question...is this the right MOSFET for a 12v 1.5amp?

Hello, I am looking at this mosfet:
**broken link removed**

http://www.radioshack.com/product.a...ame=CTLG_011_002_017_000&product_id=276-2072#

to run this gearhead motor:
http://www.futurebots.com/parts.htm
(scroll down about 1/2 way to you see this motor: #409A582)
..basicall it is a 12v 1.5amp (under load) motor.
And I want to try to power this motor via my AVR


Basically, when I read the datasheet, I got:
-the ground can be up to +-20v diff than the source (so I could have I could apply 1vDC to the Gate, and get 21vDC out of the drain).
-the max output of the drain is 60vDC
-3.0amps max output of the drain.

Am I right?

I picked the above mosfet because i can pick it up at radioshack.

I guess after I complete this easy task.. i would also want to be able to move the motor in forward/reverse and use the encoder.... but first things first (unless radio shack has the parts to do that also.. so I only have to make one trip )


thanks for any help!

Lee

Re: Newbie question...is this the right MOSFET for a 12v 1.5

IRF510 is a typical MOSFET.
The only one thing I don't like about it is its Rds(on)=0.56Ω.
For the time being you can use this one but for future selection try to find one with Rds(on)<<0.1Ω or you can connect 2(or more) of these MOSFETS in parallel.

Re: Newbie question...is this the right MOSFET for a 12v 1.5

So basically something as simple as the attached pic... (no need for extra resistors or such?)

It doesn't really matter if the PSU feeds the + or - into the MOSFET, right? Since 5v+ -12v = diff of 17v (below the 20V max).

Also, I wouldn't want to share a common ground with the AVR and motor right (since one is analog and the other is digital)?

Am I on the spot?

Re: Newbie question...is this the right MOSFET for a 12v 1.5

It is important to connect (-) to N-MOSFET S and (+) to D, as you can see on the attached drawing.
As microcontrollers are not very good in driving Mosfets, you should consider connecting some gates, for example 74HC04, in parallel and then drive this Mosfet. Between gates and AVR you may use an optocoupler..
Also, remember about diode (polarity important) accross DC motor ..

Good luck and regards ..

Re: Newbie question...is this the right MOSFET for a 12v 1.5

Thanks for the help solving the issue!

Now just have some questions

--It is important to connect (-) to N-MOSFET S and (+) to D, as you can see on the attached drawing.

I guess this is just because of how mosfets are designed.. so really no way to explain this outside of , that is how it is designed.. right?

-As microcontrollers are not very good in driving Mosfets, you should consider connecting some gates, for example 74HC04, in parallel and then drive this Mosfet.

Why are they not very good? and why does the 74C04 help?

-Between gates and AVR you may use an optocoupler..
Also good to be double safe

-Also, remember about diode (polarity important) accross DC motor ..
I have seen this done on printer motors.. and this causes the motor not to twitch, right? ... I guess i should just ask what this is for..


Heh, sorry for all the questions, but when you find someone that knows their stuff, that is rare, and I thurst for knowing all this stuff.

By the way, do you do this for a living (that is how you know all the stuff?)

thanks!
Lee

Re: Newbie question...is this the right MOSFET for a 12v 1.5

About the driving MOSFET issue: Mosfets gate represents certain capacitance. To charge it or discharge it you need significant surrent. This is because you want to switch mosfet as fas as possible, and off as fast as possible, too.
Standard microcontroller's pins are not designed to sink and source currents of this level, therefore to improve mosfets switching time one uses a driver. On that drawing you have 3 gates connected in parallel; the reason being, this configuration increases the the capability of sinking and sourcing output currents..
If you would like to read more on this topic, here is a link:
**broken link removed**

Diodes, MOSFEET and all other details you should be able to find with this forum on: driving motors, or similar topics.

Once again, good luck and regards ..

PS: you can live of this "stuff"..

hmm.. I searched the board.. and didn't find to much info on the below questions:

what value should the freewheeling diode be? does it vary per situation?

And would i still need a 74HC04 if i use the optocoupler?

I read through the pdf.. and some of it made sense.. some not :/

thanks for the help!

Added after 1 hours 23 minutes:

I guess the only thing I need to worry about on the diode is the AMP rating, right?

Added after 32 minutes:

Well.. I would have to worry about the V also, but normally the V is very high on standard diodes (like he ones i just picked up at radioshack are 1000v)

Re: Newbie question...is this the right MOSFET for a 12v 1.5

- Freewheeling diode - fast recovery diode such as UF4004, BA159 ..
Important parameters are:
trr, the samaller the better, usually 30-50ns
Ifsm, for normal 1-2A (If) diode, this current will be somewhere aroun 150-250A.
Vrrmax, most of them have at least 400V ..

- Altrnative circuit with optocoupler and two current boosting transistors is attached.
Make sure when selecting optocoupler that its Vce voltage is > than that of the power supply; otherwise you will have to use a ≈1k resistor, and ≈12V zener diode, to limit this voltage.

regards ..