Society of Robots - Robot Forum

Electronics => Electronics => Topic started by: Its_Friday on March 07, 2009, 01:09:03 PM

Title: Mosfets and H-bridge help
Post by: Its_Friday on March 07, 2009, 01:09:03 PM
I need an H-Bridge for my robot but i've never built one. Putting it together shouldn't be a problem, but choosing the right MOSFETs is proving to be difficult.

The motors are hooked up to a 12V battery.  I know i need 2 PNP, and 4 NPN MOSFETS.

I'm trying to buy the MOSFETs off of Newark but i don't know what the specifications for the MOSFETs (http://www.newark.com/jsp/search/browse.jsp;jsessionid=PVCFPCT142RYGCXDUY2W13Q?N=1001824+296254&_requestid=192300) should be.
Title: Re: Mosfets and H-bridge help
Post by: Trumpkin on March 07, 2009, 05:39:42 PM
How much current do your motors draw? You actually only need 2 PNP and 2 NPN.
Title: Re: Mosfets and H-bridge help
Post by: Its_Friday on March 07, 2009, 06:41:15 PM
My mistake about 4 NPN, i must have been looking at the wrong diagram^^'    The motors draw 111 mA at no load. Not sure about at full load. Maximum torque is 3.59 Kg/cm. 
Title: Re: Mosfets and H-bridge help
Post by: Trumpkin on March 07, 2009, 08:48:08 PM
You could just use an SN754410 http://www.sparkfun.com/commerce/product_info.php?products_id=315 (http://www.sparkfun.com/commerce/product_info.php?products_id=315) and save yourself the work of building an H-Bridge.
Title: Re: Mosfets and H-bridge help
Post by: want2learn on March 08, 2009, 03:39:02 AM
You actually only need 2 PNP and 2 NPN.

True, but you do get 6 transistor H-bridge variants.

The motors draw 111 mA at no load. 

I've used small signal transistors @12V/200mA in 6 transistor H-bridges with no apparent problems thus far.

You could just use an SN754410 and save yourself the work of building an H-Bridge.

This would be the simplest solution
Title: Re: Mosfets and H-bridge help
Post by: Its_Friday on March 08, 2009, 09:42:43 AM
Thank you for your help guys. To keep things simple, i'm getting the ICs.^^
Title: Re: Mosfets and H-bridge help
Post by: Its_Friday on March 15, 2009, 11:56:51 AM
To control the speed of the motors via PWM using the axon, do i hook up the Digital I/O pins to the IC  (http://www.sparkfun.com/datasheets/IC/SN754410.pdf)pins: 2,7,10,15?
Title: Re: Mosfets and H-bridge help
Post by: Admin on March 15, 2009, 09:10:58 PM
If you really want to simplify things just buy a full motor driver. Such as at http://www.dimensionengineering.com (http://www.dimensionengineering.com).