Step it up a notch 80v

[joecnc2006]

Pardon the PUN "Step it up a notch"

Has anyone built, building, planning, or thinking about a DIY 80v 6a-7a controllor? I would like to make them, but do not know ehere to start as far as drivers and layout etc. Would be nice to have a DIY gecko alternative people can make and easy to replace parts on them (don't get me wrong Gecko's are great drives) but you know diy is just plane fun....

Joe

[joecnc2006]

No Replies?

[mcarvey]

I am in the final stages of development of a DC servo controller using a 18F452, and am in the process of doing a writeup/webpage. Were you thinking of making a controller for a Servo Motor or a Stepper Motor?

-Matt

[sdantonio]

Joe,

Since we talked last I have done a couple of searches of the web and haven't found anything by way or a 80V stepper board schematic. For some reason people seem to be stopping at about 50V (Alan's PicStep for example). I did see a reference, and I don't remember where, that said something about not being able to go over 80V (80V being an absolute limit) due to back EMF. But I didn't read it carefully and don't remember enough of it to say for sure what the reasoning is.

Steven

[BCwanderer]

http://www.datasheetcatalog.com/data...1/IR2184.shtml
The ir2184 bridge driver is good to 600 volts.
A high voltage stepper driver should be buildable with high voltage FETs
Do you need Bi-polar or can you use unipolar stepper drivers?
Unipolar can use low side FET drivers

[NC Cams]

Check out the Servo amp/servo motor treatise on the Rutex site. Real good info.

From his treatise, in concert with some reverse engineering, here's my take:

The voltage rating is a function of several things:

1. Volatage rating of fets.

2. Whether they get power from power buss - on the regulated side of a PWM'd fet control, they seem to be essentially the same.

3. Back EMF.

Obviously, 60v fets won't work at 100 and 200v will be horrible overkill run at 60. Select accordingly and with enough capacity to handle surge current and voltage.

Back EMF can be absorbed by the epitaxial diodes inherent in the fets, if you have enough of them. It is better, however, to shunt with appropriate diodes. Make sure you have diodes w/enough voltage and current capability. Schottky's are preffered.

If the drive gets power from the same buss that feeds the motors, you usually have to double or tripple regulate to get from 180 to say 100 then to 20 and the to 12 or 5vdc that the drive circuit runs on.

A shunt regulator can do the grunt work to get from unreg to something liike 12-14vdc that an LM2940T5 will handle (these are MUCH better than 7805's - don't bypass with a diode!!!! for reverse insertion protection is in there already).

I tuned up some servo amps via using heavier versions of these very components and they seem to work fine - but you really have to dig into the controller to get to adjust current limits, over voltage, etc when you try such surgery - definitely NOT for the faint of heart nor electronically challenged...

[BCwanderer]

Here is an idea. Untested but interesting!
Has anyone tried making a high voltage bi-polar by using an allegro a3982, a3983 or a a3984 chip as a translator.
These allegro chips are available for less than $5.
If the outputs from the chip were loaded with a resistor, the current direction and step could be sensed with a fast opto-coupler.
There would need to be 4 opto-couplers, two for each "coil' connection.
The opto-couplers could drive ir2184s which in turn would drive a high power H bridge.
The allegro chip could be operated at 12 to 15 volts with low current while the H-Bridge could be operated from a high current-high voltage supply.

The chopping could be sensed by the Allegro chip by running the H bridge current through a sensing resistor which would be connected to the sense connection on the Allegro chip.
The allegro chip would be isolated from the H bridge by the optos. The common ground and the sense connection would be the only shared connections.

This could also work as a unipolar driver by having each of the optocouplers drive a low side driver FET to a unipolar motor.

The allegro chips have full, half, quarter, eighth, and sixteenth step sequencing, depending on the chip chosen.

Any ideas or comments please.

[joecnc2006]

I'm still searching, would like to stay with Bi-polar steppers, cheaper and easier for the diy. Or thats what most people understand and recognize.

Joe

[pminmo]

I presented essentially the same question to an Allegro support engineer, they won't say it can't be done, but they don't advise it either. (their bipolar parts) I'm heading down a different path as I believe there are performance gains that can be had vs. how the Allegro parts handle.
Unipolar I don't see as a problem, but again I'm going a different path there also.

[Arthur Clampitt]

Re: high voltage bipolar idea

Nice idea , but I think you might find it difficult in practice, I can't see how you would manage to feedback the current level in the extrernal transistors to the chip for control of the PWM chopping, From the simplified diagram on the data sheets , the sense resistor is needed to give the ground for the internal bridges and the sense connection is connected to the internal bridges , Trying to superimpose a voltage from sensing on the External FETs would be a problem

Bearing in mind that the block diagrams given on data sheets are highly simplified there may be a way of doing it , but you'd need more detailes circuit info

[phantomcow2]

A friend of mine made a stepper driver good for 8 amps and 100v. It was simple unipolar, good for 1/2 stepping only. Based off transistors and PIC chips. It sure worked well though

[spalm]

Couple of thoughts on higher voltage and current drivers.

You will find a cut-off of around 50 volts for the integrated type drivers (Allegro, SMC, National). These are easier to use but are usually DMOS devices. DMOS allows the chip designer to put low voltage and high(er) voltage devices on the same substrate and get a little more current ability for their output section with the requirement of using lower voltages to satisfy both types of FETs. Using P-MOS at high current also has the disadvantage that it is a bit slow, so it will run hotter.

Here’s DMOS (Dual-MOS) from Wikipedia:
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This type of switch uses one P-MOS and one N-MOS FET to counteract the limitations of the Single type switch. The FETs have their drains and sources connected in parallel, the body of the P-MOS is connected to the high potential (Vdd) and the body of the N-MOS is connected to the low potential (Gnd). To turn the switch on the gate of the P-MOS is driven to the low potential and the gate of the N-MOS is driven to the high potential. For voltages between (Vdd-Vtn) and (Gnd+Vtp) both FETs conduct the signal, for voltages less than (Gnd+Vtp) the N-MOS conducts alone and for voltages greated than (Vdd-Vtn) the P-MOS conducts alone.The only limits for this switch are the gate to source, gate to drain and source to drain voltages for both FETs, at which time the FETs are damaged.
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If you build with discrete N-MOSFETs and use a rated hi-side driver as BCwanderer mentioned, you can go as high as you want. It will cost you dollars every time you inch up voltage or current. Neat thing about discrete designs is you can pick your price/power point for every motor.
Steve