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.