MOSFET and H-bridge question? / General Science and Electronics / Forums

Forums

4hv.org :: Forums :: General Science and Electronics

« Previous topic | Next topic »

MOSFET and H-bridge question?

1 2 next

Move Thread

LAN_403

Ash Small

Thu Apr 11 2013, 02:32PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

I'm planning on running a low power (12V, 0.5A) H-bridge for some simple stepper motor experiments and I'm wondering if I can use these MOSFETs:

]51949.pdf[/file]

and use these half-bridge MOSFETs:

]fds4501h.pdf[/file]

as 'totem poles. I'm completely new to actually building this type of circuit so I may be completely mistaken here.

Also, regarding high side and low side drivers, do I need to worry about such stuff when the voltage accross the bridge is only 12V, and is well within the parameters of all components I've selected.

I'm planning on using something like 555's or something similar to drive the totem poles (half bridge MOSFETs).

Patrick

Thu Apr 11 2013, 09:27PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

really, having done things both ways, Id recommend the "power IC" type, much cheaper, easier, less headache, more features... ive used the 555 timer and individual mosfets in the way you are implying, it wasn't fun...

EDIT: L298 and L297 pairs work well, if you can afford them. [mouser sells single parts for 4.45 US$]

Ash Small

Thu Apr 11 2013, 11:31PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Patrick wrote ...

really, having done things both ways, Id recommend the "power IC" type, much cheaper, easier, less headache, more features... ive used the 555 timer and individual mosfets in the way you are implying, it wasn't fun...

EDIT: L298 and L297 pairs work well, if you can afford them. [mouser sells single parts for 4.45 US$]

I understand what you're saying, Patrick, but I'm trying to build this up from 'first principles' (I'm a masochist

)

I'm going to drive this from the I/O pins on a RasPi, I'll only be using an additional chip if I need amplification.

I reckon I can drive each H-bridge from one I/O pin, ie two pins per stepper motor...four I/O pins for two steppers (for my 'universal coil winding machine')

I'll check the ic's you reccomend in the morning when I'm sober, but the way I see it, I won't even need heatsinks for these MOSFETs at these power levels.

I've got a driver board for one of the steppers I have, but it uses an RS422 interface (an obsolete Apple interface, from what I can gather), I can get a USB adaptor for it....for Â£Â£Â£'s...but I still can't integrate it with the other stepper I have (or any of the ones I've seen on E-bay), so I want to build my own driver from 'first principles', and develop it as I go. I don't need a lot of functionality for the coil winder, but I may need more if I convert my lathe to CNC, or other similar projects.

I've also done virtually no programming for the past 30 years, but I do think the way forward here is the RasPi, controlled via WiFi from an Android smartphone.

Do you think the MOSFETs and MOSFET bridges linked to above will do the job, and do I need to worry about isolation for the high side MOSFETs?

Ash Small

Fri Apr 12 2013, 11:29AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Well, I've had a look at the datasheets and app. notes for the L298, etc. and, certainly when using the L297 as well, it looks far too complicated for my requirements at the present time.

I could possibly use the L298 on it's own for driving my motors, but it would still require far more inputs than I'd planned to use (as I said before, I can drive two steppers from four I/O pins using 'old fashioned' H-bridges).

Also, the cost of all the other components required, and complexity of the required circuit is not what I'm looking for at all.

I just want a simple H-bridge circuit that I can 'flick' between states with one I/O pin, for some basic, simple experiments with stepper motors. (I can do this by 'reversing' two of the totem poles)

While I realise I could build a driver circuit for an L298 that would achieve this, it seems a bit pointless at this stage, although I'll probably try using them later.

I think I'll stick with the original plan for now, partly because of the bigger safety margins with the voltage ratings of the MOSFETs, and partly due to the added complexity of using the L298.

Ash Small

Fri Apr 12 2013, 02:24PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Having looked again at the L297 datasheet, It looks like I can drive the two motors in my coil winder using just three I/O pins, as one only needs to rotate clockwise, so I won't need the CW/CCW input, just the clock input.

I'll need clock and CW/CCW for the second stepper though.

I don't think I need to control any of the other inputs for this application, I can just set them to whatever level they require, and leave them.

Maybe it will be simpler to use these chips instead of building four H-bridges.

I'll certainly have plenty of I/O pins left over if I want to develop it further in the future.

It's still going to be more expensive though, once I've bought all the extra diodes and everything else that these chips need.

Patrick

Fri Apr 12 2013, 05:29PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

i think your wanting the "unipolar stepper" circuit, this way you wont have the high side problem...

like here:

do you have access to all phase coil wires?

Sulaiman

Fri Apr 12 2013, 06:46PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

if you are using a 'power' stepper then you will need current control/limit for low/zero speed as the winding resistance is quite low to allow high speed stepping....
e.g. as implemented in the 297/298 combination.
This is one case where re-inventing the wheel will probably not produce better results.
Spend the time/effort/braincells on the T.C. !

Ash Small

Fri Apr 12 2013, 09:50PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Patrick wrote ...

do you have access to all phase coil wires?

If you mean the four wires that go into the stepper motor, then yes (at least on one, I've not opened up the second one yet, it has eight wires going into it though, so I'm not sure of the internal configuration yet). The first one has a built in driver circuit which I'll be scrapping, as it uses an RS422 interface. I'm not averse to buying more NEMA23 motors from Ebay, as they are cheap enough. The 'second' one I have was 99p plus postage, the first one I found in the shed.

I've built a little circuit using two DPDT switches to act as mechanical H-bridges so I can test the first stepper motor to get everything wired up correctly, and I have some 10W 22 Ohm resistors so I can limit the current to 0.5A when driven from 12V (internal resistance of each coil is ~2 Ohms, which gives a total of 24 Ohms).

I will be posting more details about this, I was just hoping to order the MOSFETs now, to save time later, however, I'm now considering using the L297/L298 chips.

The circuit you linked to Patrick will require four I/O pins, from what I can see. The circuit I originally devised only needs two per motor, one for each H-bridge, to 'flip' the state from one channel to the other.

[quote]
This is one case where re-inventing the wheel will probably not produce better results.
[/quote1365804583

I wasn't actually hoping for better results, just a very basic stepper controller, but I think I can achieve the same thing using the L297/L298, but not using all the available functions, at least to start with anyway.

Patrick

Fri Apr 12 2013, 11:20PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

if you are seeing 8 wires, I think that means 4 coils, so you can configure it externally for any driving circuit you want, like unipolar mode...

I think this is the circuit you mean :

Ash Small

Fri Apr 12 2013, 11:58PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Patrick wrote ...

if you are seeing 8 wires, I think that means 4 coils, so you can configure it externally for any driving circuit you want, like unipolar mode...

I've read up on uni-polar and bi-polar steppers, I thought one had four wires and the other had six. I did read somewhere that some have four coils, but I'll have to look into it again. I have the part number, and looked at the website, which had various configurations.

I may buy another four wire one, as I don't think I need half-stepping, or wave-stepping (or whatever it's called), or 'chopping'. I was planning on just using a basic driver, and using gears if necessary, but it might simplify things if I can use direct drive. I'm still in the planning stage.

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob