Re: Higher power from L298 etc.

Apologies, Coert - I misread your message - didn't spot that you said the
controllers had 4 L298's rather than 2. Would be interesting to know how
that is wired up.

Regards,
Tony

At 10:18 07/11/2002 +0000, you wrote:

>Yes, the SGS Thompson datasheet shows such a configuration; however,
>they indicate a max of 3A (not 4A) DC and 3.5A repetitive (80:20 duty
>cycle with n on time of 10ms) for that configuration. So it sounds to
>me like the boards you have are a touch over spec'd according to the
>words in the SGS Thompson datasheet.
>
>Operating the drivers independently, the datasheet indicates 2A/phase
>DC and 2.5A/phase repetitive. So by using an extra 297 to allow all 4
>drivers to be current limited independently, it seems to me that you
>could end up with 4A/phase DC and 5A/phase repetetive.
>
>Anyone know of/tried such a configuration?
>
>Regards,
>Tony
>
>--- In CAD_CAM_EDM_DRO@y..., Van Der Sandt Coert <vandersandtc@a...>
>wrote:
> > Hi Tony
> > I have four controllers (Avistep) that I bought surplus. Each
>controller has
> > four 298's and only one 297. Claimed current per phase is 4A. I
>could never
> > test this as none of my setups is that power hungry. My point is
>that it is
> > possible to get 4A / phase with 4 298 and one 297. Unfortunately I
>do not
> > have the circuit diagrams for the controllers only the physical
>controllers.
> >
> > BTW : Has anyone ever heard of Avistep controllers? Net searches
>don't seem
> > to be able to find any references to these controllers.
> >
> > Cheers
> > Coert
> >
> > -----Original Message-----
> > From: Tony Jeffree [mailto:tony@j...]
> >
> >
> > I was musing about the problem of getting better than 2A/phase out
>of
> > L298s (or better than 2.5A/phase out of Allegro 3977s). The
>datasheet
> > for the L298 suggests that it is possible to use 2 L298s, and
>deliver
> > 3A/phase, by paralelling the two driver stages in one 298 to drive
> > one motor coil, and paralelling the other driver stages to drive
>the
> > second coil. Presumably, you can't get the full 4A/phase when doing
> > this because of imperfect matching of the driver characteristics,
> > which would cause one driver to take more of the current, and the
> > current sense operates on the sum of the currents through each
> > driver, leading to the danger of thermal runaway & release of the
> > magic black smoke.
> >
> > It occurred to me that there is an alternative approach that could
> > work with 8-wire motors; instead of wiring the L298 outputs in
> > paralell, you use one half of a 298 to drive the A coil, and the
> > other to drive the B coil; similarly, use one half of the second
>298
> > to drive the A' coil, and the other half to drive the B' coil.
> > Unfortunately, you would have to double up on L297's as well, in
> > order to control all four coils independently; the step-and-
>direction
> > signals into these would simply be wired in paralell.
> >
> > All four drivers should then be able to operate up to their full
> > 2A/phase, as they would be generating their own independent current
> > sense signals back to their respective 297s. In effect, you would
> > then have the same result as driving the 8-wire motor in bipolar
> > paralell configuration, and would set the current limit on the
> > drivers to 1/2 the value you would normally use for bipolar
>paralell.
> >
> > Presumably this same approach could also be used with other driver
> > chipsets such as the Allegro 3977, etc.
> >
> > So this would seem allow driving up to 4A/phase into 8-wire motors
> > using two sets of 297/298, or 5A/phase using two 3977s.
> >
> > Can anyone see a problem with this approach (other than the cost of
> > an extra chipset & ancilliary components per motor, and the
> > limitation of using 8-wire motors)?
> >
> > Regards,
> > Tony
> >
> >

Regards,
Tony