Using LM317 as chopper driver for small stepper motor

Can i use an LM317 wired up as a constant current source as a chopper driver for a small stepper motor? The power supply is 24v and the current will be limited to 200mA. The way i unsestand a LM317 as a constant current source is that it will vary the voltage to ensure the constant current will go through the device. So when the motor steps the voltage will go high to initiate the step but will cut out as soon as the current reaches 200mA. So is this not do the same as a chopper driver? i understand heat might be an issue with the LM317 but for small loads like this i dont see it being an issue with a big enough heat sink.

So my real question: Is an LM 317 "simular" to a chopper driver and will it behave like a chopper driver by supplying the motor with its maximum current as fast as possible?

The lm 317 can be used as a constant current source but that as a linear regulator, not a chopper. It will get very hot since it will have to dissipate almost all the power. Also being a 3 pin regulator it has no means of being controlled by software.

nilton61: The lm 317 can be used as a constant current source but that as a linear regulator, not a chopper. It will get very hot since it will have to dissipate almost all the power. Also being a 3 pin regulator it has no means of being controlled by software.

But will the LM317 give me the same results as using a chopper? a chopper raises the voltage as high as it can to get the current flowing through the inductive load as fast as possible but chops the voltage when it reaches a set current. An LM317 is doing the exact same thing is it not?

i just want to us the LM317 as a power supply to supply the steppers with power. i am driving the steppers with N-chanel and P-chanel mosfets configured in two H-bridges

but chops the voltage when it reaches a set current. An LM317 is doing the exact same thing is it not?

No, it does not chop. As stated, the LM317 is a linear regulator.

In a chopper it is not the the regulator itself that rises the voltage but the inductor. This cannot be accomplished with a linear regulator. A linear regulator just acts as a (self varying) resistor.

I really dont understand why the LM317 will not give the same desirable "Fast current to the coils of the motor" as the chopping driver?

So the LM317 will stop the voltage at the maximum current instead of switching it off?

When used as a current source the LM 317 will sense the current through itself and vary its own resistance in order to keep the current at a constant value determined by the sensing resistance. Remember that a resistor is just a heating element converting electric energy to heat that will be lost forever.

In a chopping regulator the process is completely different. The current is switched on with neglectable resistance. Because of the nature of an inductor the current will increase gradually storing the electric energy in a magnetic field in the process. When the current has reached its preset value the regulator switches of and the energy stored in the magnetic field will be recycled through the flyback diodes. Theoretical no energy is converted to heat. In practice there in inevitable resistance in the inductor and in the switch. But these are several magnitudes smaller than the resistance of a linear regulator.

It seems to me that you really need to brush up on your understanding of the underlying physical models before attempting these things.

Why do you think im asking then? ok so if i understand your explanation correctly then, the two are different, they behave differently but the only difference in the outcome (not looking at the inner workings of the chopper and the LM317) is efficiency? If you just look at the current and the voltage the motor gets (ignoring how its generated in the back ground) then the two can be used interchangably.

I do not want to be rude but this is one huge problem with forums. If i dont understand something i will obviously google it before i ask about it. Now when i google stuff and i still dont understand i will ask in a forum. Not because the answer is not available on google (it will probably always be available on google) but because i have read the answer and yet i still struggle to understand it because of underlying concepts that i do not understand yet because i have not been exposed to them.

Now there are millions of things to understand in electronics.(for example concepts 0- 1000000). Now there is no way possible that a person can learn these things going from concept zero to 1 to 2 to 3 to 4 … in sequence. You will learn these things all mixed up like 0 to 100 to 5 to 26 … etc. So when people tell me i really need to brush up on my underlying phisical models i feel like F##KING exploding in anger!!! How can you be so narrow minded?

Sometimes the best way to understand a concept is to answer the questions you pose to yourself!!! so if i ask a question its not because i am stupid its because i am trying to answer the questions i pose to myself to understand a concept. If the questions i pose to myself are not answered then i will still most likely be confused.

If you dont like the answer you shouldnt have asked. And you are very wrong in your conceptions of physical concepts. It is not a bunch of fact that have to be memorized like a vocabulary. But its a layered model where understanding one layer relies very much on thoroughly understanding the underlying one. One reasons why books are preferable to google. What you are expressing is a result of today's short cut thinking and from that perspective it is understandable that you are perceiving electronics as "million of things to understand" There are not. I fact its the opposite there are few, but very often these few things are not understood well enough to see the structure. If we list them in a logical order:

  • The concept of energy. This is so basic and so important that it cannot be stated enough. Actually not a aprt of electronics itself but if you havent grasped this you are basically lost
  • Electrical charge and electrical fields.
  • Voltage and current and their conceptual explanation models
  • Electric circuits and Resistance, ohms and kirhoffs laws, series and parallel connections and their applications.
  • Active power in resistive circuits. Joules law and its variations and applications
  • Capacitance , its conceptual explanation models and its applications and its energy storing abilities
  • Magnetic circuits and their analogy to electric circuits.
  • Inductance its conceptual explanation models and it energy storing abilities
  • Reactive circuits, reactive and apparent power

One problem that todays short cut thinking is that many people start at point 4 instead of point 1 which leads to exactly what you are experiencing. What you are asking is on level 8 but the way you ask indicates that you are not past level 5. hence my comment.

Ok yes what you are saying is exactly correct. I did not study electronics, i only started about a year ago, building projects for fun. So i do not know the exact process flow of what to understand and grasp first before i can understand the next level. So i will in the future be all over the place in no sequence at all. This is just the way you do things when you self teach yourself. Maybe at a university they teach you basic must know concepts before the other things. Did you study electronics?

I will not learn anything if i study those things you have stated above. its simply too boring. Instead the end result of a project will attract my interest, i will then try build it and in doing so will need to learn how things work on a fundemental level, but now it wont be boring because i know i will need to understand this in order for my project to work. Its not that im taking short cuts. its like learning about pointers in C programing. you wont know why the F you are learning it and for what you will ever use it for so its most likely to bore you and you will forgrt most of it cause your not interested. But when your actually busy building something and you relize oh now i need to use pointers for this to work. then you will understand what and why a million times better.

here is an example:

"so if i understand your explanation correctly then, the two are different, they behave differently but the only difference in the outcome (not looking at the inner workings of the chopper and the LM317) is efficiency?"

I feel like i need this question answered as in : Yes or No because. This will let me confirm my current understanding of how i percieve what you are saying. But yet this happens countless times where questions like this are just ignored

calvingloster: its simply too boring.

I have some sympathy with this. I find it easier to learn things when I need to know them.

But the inevitable consequence is that I (and you) ask "ignorant" questions which can be irritating to people who know what you don't know. Getting angry is totally unproductive - just learn. And ask follow-up questions with humility rather than criticism for the teacher.

...R

calvingloster: "so if i understand your explanation correctly then, the two are different, they behave differently but the only difference in the outcome (not looking at the inner workings of the chopper and the LM317) is efficiency?"

From my limited knowledge I suspect there isn't a simple yes/no answer answer. You are asking a question like "is toast better than jam". Yes there is an obvious efficiency difference. But I don't know if there is also a performance difference. And it could well be that nobody knows because the experts "know" to use a chopper driver for stepper motors - in the same way that you "know" to put toast in the toaster and never tried putting jam into it.

I am reasonably comfortable with digital electronics - someone else gives me a device that does 1 or 0 and I don't care how that happens inside it. But an LM317 is analogue electronics and I find that a whole lot more complex - i.e. I have never bothered to study it - so I am careful to stay away from pioneering applications.

The Arduino is a great system for experimenting. You could always make a project out of answering your own question.

...R

Robin2: I have some sympathy with this. I find it easier to learn things when I need to know them.

But the inevitable consequence is that I (and you) ask "ignorant" questions which can be irritating to people who know what you don't know. Getting angry is totally unproductive - just learn. And ask follow-up questions with humility rather than criticism for the teacher.

...R

Well said, i will then in this case just continue googling and asking ignorant questions till i understand.

its simply too boring.

Do you want to learn or do you want to be entertained? I'm sorry to say this but more often than not learning involves discipline. And how you choose to perceive a certain subject is totally your own decision and your own responsibility. Certainly not your teacher's.

calvingloster:
asking ignorant questions till i understand.

Just do it nicely. Make sure to make your teachers feel good about themselves, and really important.

…R

I am an autodidact. I decided fairly early that I was going to go into electronics.

But there were no classes in electricity and electronics in 3rd grade. Even the science covered was extremely elementary (snork).

So I spent a lot of time reading books and working on building mental models. I also built projects from magazines, tearing apart broken TVs and stereos from the local appliance store for parts. It took me a while to really -get- it. That said, I do not labor under the misapprehension that I know it all. There is way too much to know all of it!

Work on it. Keep yourself interested. Read, ask questions. Stay calm, you aren't paying anyone here to teach you. Abuse a few people here, you'll find that fewer people will care to help you.

If someone says "you need to brush up on your concepts", using multiple exclamation points serves no useful purpose. Better to ask for suggestions regarding which concepts, and maybe for recommendations for websites or books. There are a lot of crap websites and Youtube videos out there. I watch a lot of basic electronics videos just to review and rate them.

As to your question, well, perhaps you might be able to jerry-rig an LM317 into something like a constant current drive for a stepper motor. But it would take some really weird circuitry, and likely still give you problems. It is designed to be a linear regulator, so it may not switch quickly enough. And as has been stated, a chopper stepper driver turns fully on and off, using the inductance of the stepper motor to store energy. An LM317 when fully on still drops about 2V across it.

So the best answer to your question is no, it won't work, don't do it. Get the right ICs, do it with circuitry designed to do the job.

I don't mean to make it seem like I learned this easily. Thinking about electronics in meaningful ways requires a lot of work. You really need to work on the mental models, and on a lot of overlapping knowledge. Did you study physics in High School?

Do you know Kirchoff's current and voltage laws? Do you know when Ohm's law applies, and when it doesn't? How about series and parallel resistors? Do you know what a first approximation is? Second, and third approximation?

I have asked others this before, no one ever answers. This leads me to think that they don't really want to learn, they want to magically turn out to be Neo. Well, Neo worked his ass off to become a fantastic programmer before he became The One, no one seems to notice that.

You don't need to go to university to learn electronics. Being an autodidact can get you as much knowledge. But it takes even greater discipline for obvious reasons. And there is no way around that. If you want to learn a godd starting point is "Introduction to Electric circuits" by Herber w jackson and Preston A White. A new copy is a bit pricey i'm afraid but there are libraries and used book stores. You do not need the latest edition, the laws of physics haven't changed much lately