Yeah, that schematic seems to be around alot. I found it many times and
figured it must do SOMEthing if all these people use it! At first I wanted to
use all N-channel MOSFETs but, even though my boat can handle alot of weight,
the extra power needed would have been way too much for it. So I decided to
spend a few extra dollars and use the P/N combination in that circuit. And
yes, I've been making sure that I hook them up right, with the correct FETs
in the correct places.

When I was getting into the ESC many weeks ago, I had the idea of hooking the
bridge up to the motor outputs of a servo and changing a few parts so that it
would proportionately control my motors (being cheap and bored, I eventually
decided to use the PIC's I already had). It may be a good idea, and if anyone
else is interested in the modifications, I found a site that shows them:
http://www.seattlerobotics.org/encoder/200009/S3003C.html

On your page (very useful page, BTW!), at "H-Bridge Theory[1]" is this page
and schematic:
http://www.cadvision.com/blanchas/hexfet/
http://www.cadvision.com/blanchas/hexfet/np-s.pdf

That's just about exactly what my circuit is now as far as connections (part
#'s are different), except for the status LED's and the diodes. Some of the
pages I've read concerning H-bridges have said that you should use the
supression diodes when switching with transistors, but that many MOSFET's
have the diodes built in and external ones are unnecessary. Should I go ahead
and drop some of these in, at least to play it safe?

-Tony


Dan Michaels wrote:

<< Tony, I didn't follow all responses of this thread, but have a
 couple of comments. First, Blanchard's ckt has been modifed and
 re-modifed a couple of times - see here:

 http://www.cadvision.com/blanchas/hexfet/h-bridge.htm
 http://www.cadvision.com/blanchas/hexfet/h-bridge.gif
 http://www.armory.com/~rstevew/Public/H-Bridges/Blanchard/nch-brdg.htm

 Secondly, some ckts to be found use all n-MOSFETs and some ckts use
 both p- and n- types. You have to be very careful which one is above
 and which is below in the h-bridge.

 Third, it is easy to swap source and drain terminals when inserting
 - esp for the upper device. Double check this last aspect. Also, I
 am not sure all schematics draw this correctly.

 I also have some other H-bridge links on my robotics page:

 http://www.oricomtech.com/robolnk2.htm#Mot2

 hope this helps,
 - dan michaels >>

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