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Electronics => Electronics => Topic started by: airman00 on September 01, 2008, 02:57:05 PM

Title: MOSFETs for Motor Control
Post by: airman00 on September 01, 2008, 02:57:05 PM

Hello

I need to switch a motor on and off via a microcontroller. It does not need to be bidirectional . I wanna use a transistor or MOSFET to switch the motor to ground.

I have two problems:
A. I don't know the exact motor current draw of the motor . I can only assume it is like 1.5 amps stall current from the picture
http://www.thetrickery.com/ama/med/elducocardfountain.jpg
B. I do not know how to find a MOSFET that can switch the current . All i find is like 200V 2amps. Does that mean up to 200V can power it  and it can switch up to 2 amps?

Can someone help me solve these problems?

Thanks,
Eric

Title: Re: MOSFETs for Motor Control
Post by: airman00 on September 01, 2008, 06:42:56 PM

For example would this MOSFET work with a signal being generated from a PIC microcontroller ( 5V ) and with the Drain getting 6V ?
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=FDP6030BL-ND

Title: Re: MOSFETs for Motor Control
Post by: RobD on September 01, 2008, 08:21:50 PM

I was just looking for almost the same specs as you   ---weeding through dozens of n and p channel datasheets lol.

The gate threshold, it says, is 1v minimum in the datasheet.  So, 5v should keep it on. 

30v max drain to source - looks good.

 
   

Title: Re: MOSFETs for Motor Control
Post by: airman00 on September 01, 2008, 09:27:22 PM

How bout this one ? The IRF630B
http://www.google.com/url?sa=t&source=web&ct=res&cd=1&url=http%3A%2F%2Fwww.fairchildsemi.com%2Fds%2FIR%2FIRF630B.pdf&ei=xrG8SMq3BJjIednX-asD&usg=AFQjCNFNWAOjw2Ieuc8FloTzhHLGQw4GZw&sig2=CQF-dhvw0Xam-V7v1EcXuw

According to the specs it can handle 9 amps ,but does that mean that if I give it straight 5V ( no pulse )  it will be able to sink the full 9V?

Voltage to gate - 5 V
Voltage to drain - 6V @ 1.5 amps
and source obviously connected to straight ground

Title: Re: MOSFETs for Motor Control
Post by: RobD on September 01, 2008, 10:36:09 PM

I don't want to steer you wrong so I'll preface this by saying I may be waay off... likely. 

But I think there's another factor to consider, and thats the Rds(on).  I don't know if the voltage drop across the drain-source would be a factor for ya or not at your current requirements. 

Also, are you asking if the mosfet could run at 9A continuous? 

Title: Re: MOSFETs for Motor Control
Post by: airman00 on September 01, 2008, 10:40:22 PM

Quote from: RobD on September 01, 2008, 10:36:09 PM

Also, are you asking if the mosfet could run at 9A continuous? 

yes but at 5V at gate .

Title: Re: MOSFETs for Motor Control
Post by: ArcMan on September 02, 2008, 10:54:53 AM

I looked at the specs for your first MOSFET choice.  It should work fine in your appication.  Just wire your micro output to the Gate pin, Source pin to ground and Drain pin to the motor's negative lead.  The 5V output will turn the MOSFET on fully.  It also has a built-in transient suppression diode, which is good.

Your motor supply voltage should not exceed the MOSFET's max Vds.  E.g. - if your controlling a 12V motor with a 30V MOSFET, you're fine.

I have designed and built a high-power H-bridge with MOSFET's, so just post any additional questions you have.

Title: Re: MOSFETs for Motor Control
Post by: airman00 on October 18, 2008, 06:23:05 PM

Quote from: ArcMan on September 02, 2008, 10:54:53 AM

I have designed and built a high-power H-bridge with MOSFET's, so just post any additional questions you have.

*Reviving old topic since I found my own topic after a search*

Can you please post a schematic of your high power H-bridge? Also how high are we talking about?
I am looking at making my own motor controller for my wheelchair motors