Stepper driver IC to > 3A ?

J

jerry

Guest
I'm looking for a stepper driver to build into a small home built cnc
system. Want to drive bipolar parallel with motor current control and at
least to quarter step capability. Allegro et al have some nice stuff (and
Samples!) up to 3A and 50v, but is there anything else able to carry
greater than 3A?

Many cheaper surplus Stepper motors in the 200oz range are available in
nema23 or nema34 but rated 5-6A or greater at 2v. Outside the commonly
available drivers. I want to build something to drive these motors at ->6A
and current limiting at 65v. Building it is the exercise, not necessarily
buying something off the shelf, like Gecko's - good as they are.

Alternatively I thought of putting mosfets after the driver to carry the
power but would lose current limiting and I have some concerns about
response at the frequencies qtrstepping and the velocities require. Simply
put ( for my use only...) looking to step at around 25ksteps per second per
axis.

tia
 
"jerry" <jerry@nospam.com> wrote in message
news:Xns94026C147DDD5jerrynospamcom@199.45.49.11...
I'm looking for a stepper driver to build into a small home built cnc
system. Want to drive bipolar parallel with motor current control and at
least to quarter step capability. Allegro et al have some nice stuff (and
Samples!) up to 3A and 50v, but is there anything else able to carry
greater than 3A?

Many cheaper surplus Stepper motors in the 200oz range are available in
nema23 or nema34 but rated 5-6A or greater at 2v. Outside the commonly
available drivers. I want to build something to drive these motors at ->6A
and current limiting at 65v. Building it is the exercise, not necessarily
buying something off the shelf, like Gecko's - good as they are.

Alternatively I thought of putting mosfets after the driver to carry the
power but would lose current limiting and I have some concerns about
response at the frequencies qtrstepping and the velocities require. Simply
put ( for my use only...) looking to step at around 25ksteps per second
per
axis.
Once you get to this sort of power, most designs use seperate FETs. There
Click to expand...
are a couple of chips that push over 3A, but not much. It is worth
realising, that using seperate transistors, in many cases doesn't prevent
the current sense connections from being used (with a lower sense resistor),
and that there are several chips that do all the 'lower current' circuitry,
and are designed to use seperate FETs (The SGS L297 for example - this can
be used with the L298, for currents up to about 2A, but with seperate FETs
or darlington transistors for much higher current). Wired using discrete
FETs, I have seen these used at over 100A. The problem is that the
fabrication technologies needed for the power stage, and the control stage,
are not compatible. The Allegro unit, is actually a 'multi-chip' solution
for this reason, but the seperate dies, are built into one case.

Best Wishes
 
"Roger Hamlett" <rogerspamignored@ttelmah.demon.co.uk> wrote in
news:bZddb.246$9m.77@newsfep1-gui.server.ntli.net:

"jerry" <jerry@nospam.com> wrote in message
news:Xns94026C147DDD5jerrynospamcom@199.45.49.11...
I'm looking for a stepper driver to build into a small home built cnc
system. Want to drive bipolar parallel with motor current control and
at least to quarter step capability. Allegro et al have some nice
stuff (and Samples!) up to 3A and 50v, but is there anything else
able to carry greater than 3A?

Many cheaper surplus Stepper motors in the 200oz range are available
in nema23 or nema34 but rated 5-6A or greater at 2v. Outside the
commonly available drivers. I want to build something to drive these
motors at ->6A and current limiting at 65v. Building it is the
exercise, not necessarily buying something off the shelf, like
Gecko's - good as they are.

Alternatively I thought of putting mosfets after the driver to carry
the power but would lose current limiting and I have some concerns
about response at the frequencies qtrstepping and the velocities
require. Simply put ( for my use only...) looking to step at around
25ksteps per second
per
axis.
Once you get to this sort of power, most designs use seperate FETs.
There are a couple of chips that push over 3A, but not much. It is
worth realising, that using seperate transistors, in many cases
doesn't prevent the current sense connections from being used (with a
lower sense resistor), and that there are several chips that do all
the 'lower current' circuitry, and are designed to use seperate FETs
(The SGS L297 for example - this can be used with the L298, for
currents up to about 2A, but with seperate FETs or darlington
transistors for much higher current). Wired using discrete FETs, I
have seen these used at over 100A. The problem is that the fabrication
technologies needed for the power stage, and the control stage, are
not compatible. The Allegro unit, is actually a 'multi-chip' solution
for this reason, but the seperate dies, are built into one case.

Best Wishes
Click to expand...
Roger, thanks for taking the time to pen a succint and useable reply. I'm
still trying to figure out how the I might use the current sense
connections as you suggest, especially since I'm trying to select a chip
in the first place. You started an interested train of thought though,
and I think I've found some fets that have the response time that would
suit.


More power means larger motors which means less tunrs per leadscrew which
means less microsteps required which means fewer fet switches per second
required.... hummm...
 
"jerry" <jerry@nospam.com> wrote in message
news:Xns94046F37CCB3Fjerrynospamcom@199.45.49.11...
"Roger Hamlett" <rogerspamignored@ttelmah.demon.co.uk> wrote in
news:bZddb.246$9m.77@newsfep1-gui.server.ntli.net:

"jerry" <jerry@nospam.com> wrote in message
news:Xns94026C147DDD5jerrynospamcom@199.45.49.11...
I'm looking for a stepper driver to build into a small home built cnc
system. Want to drive bipolar parallel with motor current control and
at least to quarter step capability. Allegro et al have some nice
stuff (and Samples!) up to 3A and 50v, but is there anything else
able to carry greater than 3A?

Many cheaper surplus Stepper motors in the 200oz range are available
in nema23 or nema34 but rated 5-6A or greater at 2v. Outside the
commonly available drivers. I want to build something to drive these
motors at ->6A and current limiting at 65v. Building it is the
exercise, not necessarily buying something off the shelf, like
Gecko's - good as they are.

Alternatively I thought of putting mosfets after the driver to carry
the power but would lose current limiting and I have some concerns
about response at the frequencies qtrstepping and the velocities
require. Simply put ( for my use only...) looking to step at around
25ksteps per second
per
axis.
Once you get to this sort of power, most designs use seperate FETs.
There are a couple of chips that push over 3A, but not much. It is
worth realising, that using seperate transistors, in many cases
doesn't prevent the current sense connections from being used (with a
lower sense resistor), and that there are several chips that do all
the 'lower current' circuitry, and are designed to use seperate FETs
(The SGS L297 for example - this can be used with the L298, for
currents up to about 2A, but with seperate FETs or darlington
transistors for much higher current). Wired using discrete FETs, I
have seen these used at over 100A. The problem is that the fabrication
technologies needed for the power stage, and the control stage, are
not compatible. The Allegro unit, is actually a 'multi-chip' solution
for this reason, but the seperate dies, are built into one case.

Best Wishes




Roger, thanks for taking the time to pen a succint and useable reply. I'm
still trying to figure out how the I might use the current sense
connections as you suggest, especially since I'm trying to select a chip
in the first place. You started an interested train of thought though,
and I think I've found some fets that have the response time that would
suit.


More power means larger motors which means less tunrs per leadscrew which
means less microsteps required which means fewer fet switches per second
required.... hummm...
The 'current sense' connections, in most cases, just have a voltage fed back
Click to expand...
into them, from resistors between the windings and ground. They then connect
internally to a comparator, and are used to 'cut' the motor drive, when the
voltage reaches a critical point (defining a specific current level). Hence
if you have a seperate 'drive' stage, you can use a sense resistor perhaps
1/5th the 'normal' value, and the cutoff won't occur until 5* the normal
current is flowing in the output stage. If you do this, without an extra
output stage, then the result is to probably blow the built in output
transistors, but provided the new output stage can take the higher current,
everything is OK.
I'd look at the L297, which is dirt cheap (it is a real 'oldy' in terms of
stepper controllers), or the L6506 (which just does the current control). If
you look at:
http://us.st.com/stonline/books/toc/an/41.htm
This is a set of 'application notes' covering this area. The first ones
cover the 'mixed technology' needed to put drivers on the same die as the
controllers, while the others cover things like using the 'controller' IC's,
with either dedicated driver IC's, or discrete transistors. The 'point'
about the L297, is that it is just a 'stepper controller', as opposed to an
integrated 'controller/driver', and is therefore easy to wire with seperate
transistors.

Best Wishes
 
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