Re: Allegro 2961 uptdate

--- In CAD_CAM_EDM_DRO@y..., "Scott M. Thomas" <scott@d...> wrote:

> So you are driving the 2961 with the 5804? Can you give more

detail? I am

> building my own setup and would like to see how others are doing it.
>
> -----Original Message-----
> From: lonnietoons@y... [mailto:lonnietoons@y...]
> Sent: Wednesday, June 27, 2001 12:03 AM
> To: CAD_CAM_EDM_DRO@y...
> Subject: [CAD_CAM_EDM_DRO] Allegro 2961 uptdate
>
>
> I have the PWM drive up and running and am doing some testing with
> a dyno, torque and speed are very good. I did run into a problem
> though and wondered if anybody had
> any ideas on how to handle it.
> Everything works very well when I turn power on first to the 5 volt
> logic power supply wich turns on the 5804 that does the stepping.
> This at the same time brings all 4 PWM chips high(High = off) on

the

> input pins (these are then tied to the 5804).
> The problem is when I turn on the 40 volt supply first then turn on
> the 5 volt it blows out some of the PWM chips. The 2961's have an
> enable pin that I have tied high to the 5 volt supply,(High on these
> enables the chip).
> Does anybody have any ideas on how to handle this, other than to be
> sure I always turn the 5v supply on first (a recipe for disaster)
> One idea I had was to use a 5v zener off of the 40volt to keep the
> inputs of the 2961's high when the 5v supply is off line.
> Lonnie
>

Sure Scott. The 5804 is a unipolar driver that gives exactly the right
stepping sequence to drive 4 of the 2961's for a full bridge bi-polar
drive. If you do not need more that 3 amps per phase then the 2962 or
one of the newer 3000 series Allegro chips would be a better choice
because they have 2 chips in a package and I think they take care of
the cross conducting problem that can burn out chips if your timing
isn't quite right.
For an update on the above problem, I did take a zener off of the 40
volts to hold the step pins high and a pnp resistor to shut that
power off when the 5 volt comes on line. I also tied the enable pins
low thru a resistor. This all worked well. I think I will still run
the 40 volt with a relay just to be safe.
I have got the 540 oz/in motors up to 5800 steps/sec, but usually
they stall out before 3000.
I have some smaller 140 oz/in 6 wire motors(half connected) that
stall out around 1300. If I carefully accelerate thru 1300 then it
goes on up to 8000.
I have tried changing some things but no help.
Does anybody know any tricks that help with this mid-range
instability?
Lonnie