Creating a chopper drive with discrete components using the L297

[tpworks]

Originally posted by Ferenczyg
The chopper control 'only' provides the frequency of control signals for the power stage. You can use phase chopping for discrete semiconductors, or inhibit chopping signals for the non discrete IC's like l298 or l6203.

If you use discrete bridge, try to use a rsense value to create about 1V of Vsense, that is about 0.125 ohm for 8A. Reccomended chopping freq is about 20Khz. Because chopping is created comparing vsense to vref, you want to put vref about 1v, typically with a 1 to 5 voltage divider from the logic voltage.

More details, images and accuracy @ http://www.st.com/stonline/books/pdf/docs/1734.pdf

hope it helps

Fer

What chip do you recommend I use for an AND gate?
will the 74LS09 work, a Quad 2-input AND gate with open collector?

[Ferenczyg]

Why open collector? You will need pullups then..

BTW, I beware you about myself not having build a discrete Hbridge controlled by a L297, I'm struggling with a one side pcb L297+L298 design for the OpenSource CNC and a L297+L6203 design for my own pleasure by now. So plz do not trust blindly in me, if any release of magic smoke to the atmosphere occurs and is not from my own semiconductors I will feel very guilty

The main info I handle about using discretes is from the ST datasheets. In the datasheet of the quote (fig 17 by example) you need a negate signal for every phase, so I think you will need a 74LS04 too..

Fer

[tpworks]

Fer,
same here , I have built several unipolar motor controllers starting with (Luberth's design) my first about 3 years ago for my first pcb mill. Then I came across the 5804 . But you know how it goes, I got the fever and have to go bigger stronger faster, sure don't plan on putting no 6 mill into it though.
I have these huge bipolar motors I am determined to make a driver for. There is nothing more gratifying than to be able to say " I made that with my own two hands". so everything I learn is from reading looking and listening, and a little common sense thrown in . So any info is always appreciated no matter what your credentials, I think we are all here to help one another and share our knowledge and expierences even if they do produce a little smoke now and then.

Tom

[tpworks]

Any input here will be greatly appreciated and when I finish the artwork I will post a link to it here.
so far I gather I need a 7408 Quad two input AND gate,
7404 Hex inverter(although I don't see where this fits in the block diagram of the L298)
L297 step/dir chopper driver
I am going to use IRF540 and IRF9540 because I already have a quantity of these. On the block diagram for the L298 it shows a little circle on the input of two of the and gates anyone know what this is?
Tom

[lt paul]

the circle indicates an inverter

[pminmo]

Originally posted by tpworks
Any input here will be greatly appreciated and when I finish the artwork I will post a link to it here.
so far I gather I need a 7408 Quad two input AND gate,
7404 Hex inverter(although I don't see where this fits in the block diagram of the L298)
L297 step/dir chopper driver
I am going to use IRF540 and IRF9540 because I already have a quantity of these. On the block diagram for the L298 it shows a little circle on the input of two of the and gates anyone know what this is?
Tom

I really wouldn't use old ttl, if you want use the 74HC series, but in reality I would use the 4000 series cmos because of noise immunity. Have you looked at the open source driver thread?

Tools for the project

specifically this one of mine:
http://www.cnczone.com/forums/showth...2870#post32870

It has a link to Eagle files that could be the start of your design.

Why do you want to use discrete components, higher voltage, current, how much? Have you considered two 298's as they can be paralled for higher current drive.
The other point I would make is making a discrete chopper will be much more of a challenge than the unipolar drivers you mentioned.

Phil

[tpworks]

Phil,
I need 8 amps and as cheap as possible
Tom

[pminmo]

That would take 3 298's in parallel. Your probably headed down the right path with discretes. Make sure your PC layout is appropriate. Plenty of copper in the high current paths, plenty of copper for the current sense resistors.

Phil

[tpworks]

Is the 4081 (buffered AND GATE) a replacement for the 7408 acceptable
and the 4069 (Hex Inverter) for the 7404?

Tom

[pminmo]

Probably, my only concern is the guaranteed high level input voltage vs the L297. 99.8% sure it won't be a problem, but you might want to check out the 74HC series to see if they are pinout compatable just in case. The L297 Vout High guaranteed min is 3.9V, but that's at a much higer current load than the 40xx cmos will be. The Vin High guaranteed min is 4.0V (Assuming 5VDC power). For the inverter the 40106 I believe has a little lower input voltage spec.

Phil

[tpworks]

This is what I have so far (Eagle version 4.11 schematic)
just rename dropping the .txt part

I'll have to redo this and remove the file as it is corrupt I can't open it either.

[pminmo]

tpworks, I can't get it to open with 4.11. I'm doing a save target as from ie and dropping the .txt ok. But eagle says the file is corrupted. tried it twice.

Phil