Re: L297/L298 And a "correction"

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "ballendo" <ballendo@...> wrote:

>
> Phil,
>
> Snips, inserts follow...
>
> >In CCED, "Phil Mattison" <mattison20@> wrote:
> >I've looked at the IR2101 but it's fairly expensive and drives up the
> >component count since you need 4 for a bipolar stepper driver (or 2
> >of the dual version).
>
> Well, you asked for a solution to driving FET's easily and
> inexpensively; and that one is IMO one of the best...
>
> FWIW (since others will be reading these messages), Mariss has posted
> a circuit for FET driving that he says works well, and while it does
> have higher component count, it IS buildable by folks who don't want
> to use the IR210x chip(s). AIRC, it's in the files section here at
> CCED or in my DIY-CNC group.

Mariss' circuit can be found in the CAD_CAM_EDM_DRO files
section:

Files->CIRCUITS->Miscellaneous Circuits->mosfet bridge drive.pdf

[snip]

> >I understood what Wayne meant by "bipolar" (as opposed to MOS).
>
> I am sure that YOU did. But I'll bet that literally hundreds of folks
> here did not; the distinction between bipolar JUNCTION transistors
> and BIPOLAR stepper drive topology is non-obvious to someone new to
> all this. And "bipolar" to most of these CNC folks will refer to
> drives, NOT transistor type. Which IMO makes it reasonable to let
> THEM know the difference...

I agree with ballendo many people on this list do not the
difference between PNP/NPN bipolar junction transistors
and power MOSFET transistors. Thus, it is reasonable to
mention the differences between them.

The following text snippet is from the "H Bridge Selection"
section of my design notes at:

<http://gramlich.net/projects/cnc/axis4/rev_a/design_notes.html>


H-Bridge Selection

When it comes to choosing H-Bridge IC's, there are some
hard choices to make. It is fairly easy to take 8 IRF640
MOSFET's and build a couple of very powerful H-Bridges
that work in the 18 amp range. Since IRF64's are available
for about ~$.70/each, it is hard to justify spending much
more than $6-$7 per axis. There are very few H-Bridge
solutions at that price point. All I found were the A3977
and the good old L298. While I like the A3977, they do not
have a very good selection of application notes. In
particular, I could not really figure out how they wanted
to deal with excess heat generation. Conversely, the L298's
are quite easy, just slap a heat sink on. Maybe in some
future revsion of this controller I will switch over the
the A3977, but not for this revision. L298's are available
from Jameco for $2.98. A heat sink specifically designed
for the L298 Multiwatt-15 package is the 532-566010B34
available from Mouser.

This was written about 2 years ago, so it is possible that
some new <$10/axis integrated MOSFET solution has been
deployed. I certainly am not aware of any, but I haven't
beeen looking recently.

Hopefully the text above will be useful to some people.

-Wayne