Re: Allegro 3977 with separate H bridge

I've been hesitant to reply because this is one of the areas that
I'm really not sure about. However,

The A3977 has a "Syncronous Rectification" setting. This allows you
to run the motors without external schottky diodes. If you turn it
off and supply external schottkys, you take much of the heat load
off the A3977. You might be able to run higher currents since you've
taken away half the heat load (sinking).

Then of course, you'd also have to fool the current sensing -
perhaps a simple parallel resistor setup?

I dunno, the experts would have to say if this was feasable or not.
Personally, I'd be too scared to try and run 4A through the chip -
even if its only one way.

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "jc56au" <jcamp@c...> wrote:
> In looking at stepper drivers for a variety of (unpurchased but one
> of
> the cheap alternatives is 4A) motors, I was discussing various
> alternatives with one of the engineers at work who has had a fair
bit
> of experience with high power switchmode supplies.
>
> One suggestion was to use the Allegro 3977 chip with the outlets
> driving a separate H bridge (via some simple logic) and using the
> sense inputs (with appropriate resistors/capacitors) to give the
> current control.
>
> Is this a suitable method for getting the advantages of this type
of
> PWM control with minimum development effort. Obvious possible
> problems
> relate to RFI feedback and general messing around with something I
> have only a limited theorectical knowledge of.