Re: Higher power from L298 etc.

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
>
>
>
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