Re: [CAD_CAM_EDM_DRO] Re: L297/L298 And a "correction"

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). Sure the IRFL MOSFETs have a 5-volt gate but that's relative
to the source terminal so you still have the same translation problem for
the high-side switches (and the low side as well if you have a sense
resistor in series.) I understood what Wayne meant by "bipolar" (as opposed
to MOS).
--
Phil Mattison
http://www.ohmikron.com/

----- Original Message -----
From: ballendo <ballendo@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Friday, August 04, 2006 2:59 PM
Subject: [CAD_CAM_EDM_DRO] Re: L297/L298 And a "correction"


> Phil, Snips, inserts follow...
>
> >In CCED, "Phil Mattison" <mattison20@...> wrote:
> >You make some good points. I was looking at the L298 mainly because
> >it's cheap and abundant.
>
> And well proven. Used within its limits it is robust and reliable
> over the long term.
>
> >I've seriously considered going to discreet MOSFETs but the gate
> >drive requirements for the high-voltage MOSFETs looks like a real
> >pain in the keester.
>
> Here is the datasheet to a commonly used solution:
>
> http://www.promelec.ru/pdf/ir2101.pdf#search='IR2101%20mosfet%
> 20driver'
>
> >Sure would be nice if you could get discreet high-voltage MOSFETs
> >with built-in gate drivers to accept logic-level control signals.
> >Haven't been able to find anything like that. Anyone seen such an
> >animal?
>
> I don't know about a "built in gate driver" per se, but "logic level"
> FET's are pretty common. Look for an "L" in the part number--IRFL vs.
> IRF.
> Problem is they're not as good for our use, with higher RDSon and
> slower switching (more heat). But there are more than a few designs
> which use them "successfully". Like all electronic design, you have
> to assess the tradeoffs and choose your choices<G>
>
> >a 1024-step shaft encoder seems like major overkill to me. Most
> >hobbyists seem to be looking for bargains, and overkill is counter-
> >productive in that quest.
>
> Yes. But the 1024 they might want to use is BECAUSE they got it cheap
> as surplus...
>
> Ballendo
>
> P.S. I want to add something to what Wayne said; because some folks
> might find it confusing: He said the L298 is a "bi-polar device"
> which is why it runs hotter... Well, it IS a bipolar device, in that
> it changes the direction of current in the motor coil(compared to
> unipolar which does not); BUT...
>
> Perhaps a better way to say this is that the L298 uses bipolar
> JUNCTION transistors in its outputs, and it is the use of these BJT's-
> -instead of cooler running MOSFETS--which causes/creates the higher
> temps.
>
> 298's do run hot; but as long as they're properly sized for the app,
> and if needed, heatsinked; they are a good driver chip.
>
>
>
>
>
>
>
>
> Addresses:
> FAQ: http://www.ktmarketing.com/faq.html
> FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
> Post Messages: CAD_CAM_EDM_DRO@yahoogroups.com
>
> Subscribe: CAD_CAM_EDM_DRO-subscribe@yahoogroups.com
> Unsubscribe: CAD_CAM_EDM_DRO-unsubscribe@yahoogroups.com
> List owner: CAD_CAM_EDM_DRO-owner@yahoogroups.com, wanliker@...,
timg@...
> Moderator: pentam@... indigo_red@... davemucha@...
[Moderators]
> URL to this group: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO
>
> OFF Topic POSTS: General Machining
> If you wish to post on unlimited OT subjects goto:
aol://5863:126/rec.crafts.metalworking or go thru Google.com to reach it if
you have trouble.
> http://www.metalworking.com/news_servers.html
>
> http://groups.yahoo.com/group/jobshophomeshop I consider this to be a
sister site to the CCED group, as many of the same members are there, for OT
subjects, that are not allowed on the CCED list.
>
> NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM.
DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........
> bill
> List Mom
> List Owner
>
>
> Yahoo! Groups Links
>
>
>
>
>
>
>