uln2003 data sheet question.

[Dude22]

What I am trying to do.

I have built a cnc, that I can successfully run off of 500ma. But I would work a lot better if I could run it using more power, My original idea was to use a computer power supply, but my controller (uln2003's) Is limited to 500ma. The best solution would be to parallel the uln2003's as I now know it possible from earlier answers on this thread. My question now it how would I parallel the chips???

 

[CocaCola]

My question now it how would I parallel the chips???

Do you know what parallel means? If so you look at that datasheet and simply wire all the ins and outs in parallel, like so...

 

[gorgon]

And you can't drive that contraption from a normal logic output. Each ULN driver need some current to work, the internal resistors draw between 1 and 2 mA at 5V input. With 14 inputs you'll need 15-30mA in total to activate the drivers.

The max total power loss in each chip indicates a total of 1.2- 1.5 A from each chip, or a grand total of 2.5-3A. The driver outputs will drop around 1-1.5V.

Why not go for a MOSFET transistor able to deliver the current you need?

TOK

 

[CocaCola]

Why not go for a MOSFET transistor able to deliver the current you need?

I agree, that was my original suggestion back on page one, it's simply not effective or efficient to parallel these chips vs just getting a single chip that does the job...

 

[CDRIVE]

If we're taking votes I'm in the MOSFET column too.

Chris

 

[Rleo6965]

If we're taking votes I'm in the MOSFET column too.

Chris

Same here.

 

[CDRIVE]

Same here.

That Kitty is absolutely adorable! No illusions though. In about 6 months time it would eat my face!

Chris

 

[Dude22]

MOSFET

I am open to ideas but I do not quite understand how a MOSFET would work to control steppers... I have found a few examples by searching Google, but all of those used many other components. Is there any way to use ONLY MOSFET's???

 

[(*steve*)]

A single mosfet pretty much works like a single channel of a ULN2003, except some can handle upwards of 100A.

We'd need to see what you're doing to make a sensible assessment.

Do you have a circuit diagram?

 

[Dude22]

A single mosfet pretty much works like a single channel of a ULN2003, except some can handle upwards of 100A.

We'd need to see what you're doing to make a sensible assessment.

Do you have a circuit diagram?

Here is a link to a circuit diagram: http://electronics-diy.com/schematics/stepper_motor.jpg If there is any way to do this with MOSFET's then that would be great.

 

[CDRIVE]

Hi, Is there any way to lower a 12 volt supply to 500ma when it starts around 10amps???

Hey Dude, what do you mean "starts around 10A"?

I mean the original amperage is 10 and i want it to be 500ma

I have built a cnc, that I can successfully run off of 500ma. But I would work a lot better if I could run it using more power, My original idea was to use a computer power supply, but my controller (uln2003's) Is limited to 500ma. The best solution would be to parallel the uln2003's as I now know it possible from earlier answers on this thread. My question now it how would I parallel the chips???

Why not go for a MOSFET transistor able to deliver the current you need?

TOK

I am open to ideas but I do not quite understand how a MOSFET would work to control steppers... I have found a few examples by searching Google, but all of those used many other components. Is there any way to use ONLY MOSFET's???

A single mosfet pretty much works like a single channel of a ULN2003, except some can handle upwards of 100A.

We'd need to see what you're doing to make a sensible assessment.

Do you have a circuit diagram?

I thought it would be fun to post the progression of this thread, starting from post 1.

Dude22, please note your statement that I've emboldened. It begs this question:

What's the current capability of your power supply? You said that your original idea was to replace the PSU with a computer PS. Did you? If your supply can't deliver the current you need, all the FET's in the world aren't going to solve your problem.

Chris

 

[Dude22]

Power Suply

My current power suply is a 12 volt 10 amp computer power supply, but
I am also working on (as a side project) building a Variable power supply 0-45v and 0-2 amps. I want to drive the motors at 2 amps. compleatly ignoring the power suply as I will eventually be using the variable power supply anyways. would the best way to do this be with MOSFET's or ULN2003's and how woud the wireing be done.

 

[CocaCola]

I want to drive the motors at 2 amps.

Why? What are the motors rated for? Starving them and not providing what they want is not the best approach, why do you want to do this?

 

[Dude22]

Why? What are the motors rated for? Starving them and not providing what they want is not the best approach, why do you want to do this?

ture true, I will try to find the exact amperage, The reason I said 2 is that I know they work with 500ma, and as they will only take what they need I thought that 2 would be enough, but I will try to find the exact amperage draw. I will post with what I have found later.

 

[CDRIVE]

I will try to find the exact amperage draw. I will post with what I have found later.

To get an accurate measurement you need to bypass the ULN2003 and have that motor under loaded conditions. If it's possible to find yourself in an unexpected stalled condition, that should be tested too. Is this a lathe or mill?

Chris

 

[CocaCola]

Since it's a DIY CNC are these standard NEMA sized steppers? If so what number are they example (NEMA 17 or NEMA 23), from there we can get a good estimate of the ratings... If you don't know the number measure across the housings face in inches, if it's 1.6 x 1.6 it's a NEMA 17, if it's 2.2 x 2.2 it's a NEMA 23...

 

[Dude22]

Since it's a DIY CNC are these standard NEMA sized steppers? If so what number are they example (NEMA 17 or NEMA 23), from there we can get a good estimate of the ratings... If you don't know the number measure across the housings face in inches, if it's 1.6 x 1.6 it's a NEMA 17, if it's 2.2 x 2.2 it's a NEMA 23...

Its a NEMA 23

 

[Dude22]

I think mine is around: Voltage: 50V 2.8A

 

[CocaCola]

NEMA 23s range from about 2.5A to 6.0A if you don't have the specs for your exact one than it's best to aim for the highest value to be safe... Thus in this case you are looking at building a circuit that can supply and handle about 7.0A per channel...

Now remember if this is a 2 Axis the power supply should be able to run both motors at full capacity, thus you would want a 14A or so power supply... If it's 3 Axis you want a 21A or so power supply... This will allow all motors to be running at the same time...

If you picked up cheap NEMA 23s they are probably the low torque ones, and they are likely in the 2.5-3.0 Amp range but that is just a guess...

 

[Dude22]

NEMA 23s range from about 2.5A to 6.0A if you don't have the specs for your exact one than it's best to aim for the highest value to be safe... Thus in this case you are looking at building a circuit that can supply and handle about 7.0A per channel...

Now remember if this is a 2 Axis the power supply should be able to run both motors at full capacity, thus you would want a 14A or so power supply... If it's 3 Axis you want a 21A or so power supply... This will allow all motors to be running at the same time...

If you picked up cheap NEMA 23s they are probably the low torque ones, and they are likely in the 2.5-3.0 Amp range but that is just a guess...

So, how would I build a driver that would allow me to use a 20 amp power supply, and what would you recomend for the power supply.