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Author Topic: MOSFET/IGBT based full bridge motor driver  (Read 2895 times)

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Offline ambcorp2000Topic starter

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MOSFET/IGBT based full bridge motor driver
« on: October 03, 2011, 12:25:30 AM »
I used to be an industry expert on MOSFET/IGBT a long time ago but do not claim to be anywhere near that anymore. I have seen motor drivers sold for $30+ and it seems a lot to me. I was wondering if anyone here has a schematic of a MOSFET based successful driver that is reversible and also integrates motor breaking. I could design one pretty fast but gone are the days of discrete electronics that I used to design the bootstrapped drivers of the top 2 n-channel MOSFETs of the H-bridge. I searched eBay hoping to get to an IC based full H-Driver but could only get to A3986SLDT and this thing is kind of overpriced. I will appreciate if someone can suggest a cheaper alternative. Thanks!!

Offline Fr0stAngel

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Re: MOSFET/IGBT based full bridge motor driver
« Reply #1 on: October 03, 2011, 11:18:48 AM »
umm...  could you be more specific in your needs? like what would be the maximum current draw for your project?

if its not much, then try looking for "L293D" and "L298" motor drivers...
'crazy' is the new hype! =)

Offline joe61

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Re: MOSFET/IGBT based full bridge motor driver
« Reply #2 on: October 03, 2011, 11:28:43 AM »
Maybe this will help http://www.bobblick.com/techref/projects/hbridge/hbridge.html

I think I got that from Soren, if so it's probably a good design.

Joe

Offline ambcorp2000Topic starter

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Re: MOSFET/IGBT based full bridge motor driver
« Reply #3 on: October 03, 2011, 01:24:41 PM »
The issue with the darlington pair is that the voltage across the device Vce is typically 0.5V. In a H-Bridge there are 2 of them and you lost a volt. This means that a 6V battery just lost 17% of its power. I do not wish to have 2 batteries in my robot because there are several great 6V motors available that serve my purppse. MOSFET unlike a transistor is a voltage device and as long as my voltage and current ratings or my rise and fall times are not exceptional, the same driver circuit will work with a veriety of MOSFETs. All I need to do is to figure an IC that is capable of driving a full H-brigde. Once this is done, I should just be able to pick an IRFZ stereotype MOSFET and complete the circuit design. This problem is a very common one faced by and power electronics professional and I am hoping to get hold of any of them who might be on this forum. We are all software pros here but looking for that one black sheep here :-)

If it helps the discussion, the current rating is 6A but when a motor is starting up it takes 5x more current?

Offline Soeren

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Re: MOSFET/IGBT based full bridge motor driver
« Reply #4 on: October 03, 2011, 03:49:04 PM »
Hi,

I used to be an industry expert on MOSFET/IGBT a long time ago
[...]
I could design one pretty fast but gone are the days of discrete electronics that I used to design the bootstrapped drivers of the top 2 n-channel MOSFETs of the H-bridge.
Well, most pro's (even if they don't call themselves industry experts) use P-ch. transistors at the top of a bridge ;)

I'm not sure what kind of discrete components you are having trouble finding(?), but do consider doing it with P-ch. at the top and you won't need a DC-DC converter to make things happen - that should help set things in motion :)


I searched eBay hoping to get to an IC based full H-Driver but could only get to A3986SLDT and this thing is kind of overpriced. I will appreciate if someone can suggest a cheaper alternative. Thanks!!
eBay isn't (and will never be) the pro's choice for parts.
An H-bridge for a 6A motor is small potatoes when made with discrete transistors anyway and that way you know each bit of it (and can change anything if needed). Integrated drivers, OTOH, are "use once" devices.

Start current should be about twice that, so perhaps opt for 15A as a first design goal and perhaps add an overcurrent protection to avoid burning t the windings of the motor(s).
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline ambcorp2000Topic starter

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Re: MOSFET/IGBT based full bridge motor driver
« Reply #5 on: October 04, 2011, 02:03:23 PM »
I completely agree that many pros use p-channel BJTs for H-bridges because that is a simple and proven solution. I understand all the advantages of doing that but with p and n channel BJTs efficient utilization of a 6V system can be ruled out. eBay is not and probably never be the source of parts for pros but whenever I do a generic search on data sheets and application notes for a H-bridge driver, I am stuck with useless crap on websites like datasheetcatalog, alldatasheet, datasheetarchive besides others (5 years ago I remember hitting much better info on Google but it is not that simple any more I believe) so had tried a few searches on eBay that did seem to get me somewhere - I therefore welcome any suggestions in this regard.

Offline ambcorp2000Topic starter

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Re: MOSFET/IGBT based full bridge motor driver
« Reply #6 on: October 04, 2011, 04:22:34 PM »
This is a relatively inexpensive motor driver that does not use darlington pair transitors. I still do not like it since it uses p-channel MOSFETs not the best of design decisions. I will keep looking and updating improved versions as I am able to find/design them....

IN4001 diodes shown in the design are kind of hillarious to me for they are not fast recovery schottkey ones... these can be dropped since MOSFETs come with a built in free-wheeling diode...there are design flaws but the idea is very workable. Other one I noticed is that the zener is 15V but the regulated voltage that they produce is 12V.....!!
« Last Edit: October 04, 2011, 04:26:55 PM by ambcorp2000 »

Offline Soeren

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Re: MOSFET/IGBT based full bridge motor driver
« Reply #7 on: October 05, 2011, 05:53:50 PM »
Hi,

I completely agree that many pros use p-channel BJTs for H-bridges because that is a simple and proven solution.
I never said that and I think you have to search long and hard to find any that do and not only because P-channel BjT's don't exist!   ;)


I understand all the advantages of doing that but with p and n channel BJTs efficient utilization of a 6V system can be ruled out.
Perhaps you should have left out your initial (and quite pretentious) "I used to be an industry expert on MOSFET/IGBT [...]", since you seem pretty ignorant about transistors and keeps confusing them, coming off as a rank beginner.
MOSFET's, IGBT's (which aren't relevant at all in 6V systems) and BjT's are all transistors (hence the trailing "T"
MOSFET = Metal Oxide Semiconductor Field Effect Transistor
IGBT = Insulated Gate Bipolar Transistor
BjT = Bipolar Junction Transistor

I wonder why so many people find it so hard to see a MOSFET as a transistor. Using the word transistor is in itself uncommitted to the topology, but an industry expert should have caught on when reading a prefix like P-ch, which is only found in MOSFET's (the BjT equivalent is PNP).


With that done away with, please reread my former post.


eBay is not and probably never be the source of parts for pros but whenever I do a generic search on data sheets and application notes for a H-bridge driver, I am stuck with useless crap on websites like datasheetcatalog, alldatasheet, datasheetarchive besides others (5 years ago I remember hitting much better info on Google but it is not that simple any more I believe) so had tried a few searches on eBay that did seem to get me somewhere - I therefore welcome any suggestions in this regard.
Yes, there's more noise each year, but when the going gets tough... You need to know how to get the search engines to put out - a single type number might not get you too far, but most search engines have their own tutorials on how to get better results.

I don't know why you're spending time on Google for this however, as hitting the manufacturers web sites will yield more and better results  :-\


This is a relatively inexpensive motor driver that does not use darlington pair transitors. I still do not like it since it uses p-channel MOSFETs not the best of design decisions. I will keep looking and updating improved versions as I am able to find/design them....
Well, P-channel MOSFET's on the high side IS the best design decision and has always been, although it wasn't used much in the eighties due to the production costs and lack of high current p-ch. devices. That problem is gone these days.

You might try to outsmart reality, but I seriously doubt that it will net you anything but worries ;D


IN4001 diodes shown in the design are kind of hillarious to me for they are not fast recovery schottkey ones... these can be dropped since MOSFETs come with a built in free-wheeling diode...
Granted, 1N400n diodes are slow as molasses, but it's even more hilarious to call the intrinsic MOSFET body diode a free wheeling diode.
Have you really been working with MOSFET's and have you ever actually measured the degree of protection an 1N400n diodes give, or are you just copy/pasting other peoples ideas?


there are design flaws but the idea is very workable.
To quote Bill Gates (on the P-ch. devices on top), it's not a flaw, it's a feature (and this one really is ;D)
I think the flaws you find are more of what we use to call an "Error 40" on this side of the pond (which in imperial units would be closer to an "Error 16"   :D


Other one I noticed is that the zener is 15V but the regulated voltage that they produce is 12V.....!!
Hmmm, for each line you write, I doubt your "industrial expertise" more and more and if you don't know why there's a 15V zener in that position, you really need to read up on basics.

But... You claimed "I could design one pretty fast"!
Why not do exactly that (it will be much faster than searching for other peoples designs) and post it here with component values and we can then point you to where you can get the components or their equivalents - and make sure it's not dangerous for you to actually power up  ;)
That should be a great opportunity to show off some of your expertise as well :)
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline ambcorp2000Topic starter

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Re: MOSFET/IGBT based full bridge motor driver
« Reply #8 on: October 05, 2011, 08:29:20 PM »
I will be able to provide a fair opportunity to all responders to evaluate my design.... :)

I am not designing as yet cos my requirements are creeping... today for instance I added active breaking to my list cos I am new to robotics....

Offline ambcorp2000Topic starter

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Re: MOSFET/IGBT based full bridge motor driver
« Reply #9 on: October 05, 2011, 11:26:23 PM »
About the perception of a transistor, any 3 terminal device that transfers resistance is a transistor but the similarity ends there. MOSFET and IGBT are much more sensitive (especially for static electricity), have a positive temperature coeffecient and international rectifiers made them into Hexagonal structures calling them Hexfets to be able to reduce Rds to the level of milliohms. MOSFETs can pack 10s of watts into a TO-220 pack compared to a few watts by BjTs. BjTs always drop a good fraction of a volt as Vce at saturation for currents ranging a few amperes, this can be anywhere from 0.2-0.5V as discussed above. Transistors are generally slow and Cbe for a BjT is not as significant as the Cgs of a MOSFET (terminologies hold good for n-channel/n-p-n). Additionally while MOSFET is a voltage device (cos Igs = 0, transistor is primarily a current device, and therefore gain is measured in terms of current in the former, it is measured in terms of voltage gain for MOSFETs)

So to the untrained eye, a MOSFET in a typical TO-220 pack will look the same as a darlington in the same package.... but for a good designer that similarity ends with PCB layout design. Even the heat sink design in terms of degree kelvin/watt is different for both.

So while a hobbist buys the standard products and puts them together, a designer has to look more from the first principles. I realize that there has been a lot of talk and no real work on this thread.... however if someone is keen on making a point, they are more than welcome to comment on alternatives like the thyristors or SCRs, full and half H-bridge, synchronous and asynchronous commutation techniques instead of merely the 'spell checks' and probably also reduce the 'muscle flex'. I do not say that out of rage but because i have seen that individual provide great advice on this and other threads and also get a just a bit emotional which has no place in robotics since a robot with emotions has not been created as yet  ;D
« Last Edit: October 06, 2011, 01:57:30 PM by ambcorp2000 »

Offline Soeren

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Re: MOSFET/IGBT based full bridge motor driver
« Reply #10 on: October 06, 2011, 04:18:17 PM »
About the perception of a transistor, any 3 terminal device that transfers resistance is a transistor but the similarity ends there. MOSFET and IGBT are much more sensitive (especially for static electricity), have a positive temperature coeffecient and international rectifiers made them into Hexagonal structures calling them Hexfets to be able to reduce Rds to the level of milliohms. MOSFETs can pack 10s of watts into a TO-220 pack compared to a few watts by BjTs. BjTs always drop a good fraction of a volt as Vce at saturation for currents ranging a few amperes, this can be anywhere from 0.2-0.5V as discussed above. Transistors are generally slow and Cbe for a BjT is not as significant as the Cgs of a MOSFET (terminologies hold good for n-channel/n-p-n). Additionally while MOSFET is a voltage device (cos Igs = 0, transistor is primarily a current device, and therefore gain is measured in terms of current in the former, it is measured in terms of voltage gain for MOSFETs)

So to the untrained eye, a MOSFET in a typical TO-220 pack will look the same as a darlington in the same package.... but for a good designer that similarity ends with PCB layout design. Even the heat sink design in terms of degree kelvin/watt is different for both.

So while a hobbist buys the standard products and puts them together, a designer has to look more from the first principles. I realize that there has been a lot of talk and no real work on this thread.... however if someone is keen on making a point, they are more than welcome to comment on alternatives like the thyristors or SCRs, full and half H-bridge, synchronous and asynchronous commutation techniques instead of merely the 'spell checks' and probably also reduce the 'muscle flex'. I do not say that out of rage but because i have seen that individual provide great advice on this and other threads and also get a just a bit emotional which has no place in robotics since a robot with emotions has not been created as yet  ;D
Well, I don't get emotional, but when people start off by "I'm an industrial expert" and continues by rambling like a rank beginner I do find it odd.
And when claiming "I could design one pretty fast" and then want other people to do it, I do find it odd.
And when the excuse for this is that the components have somehow vanished from the market, I do find it odd.

Since we're talking discretes, anything you could get in the eighties, you can get today, either in their original form or in improved versions, so claiming that they have disappeared is a strange way of explaining why you are restrained from the "fast design" you mentioned.
That's just the main odd stuff in your posts that makes me question if you're just trying to get someone do your footwork.

I shall refrain from "spell checking" your last post, partly because you seem extremely sensitive to the truth and partly because it is a huge task. your post was amusing, but it is seldom I read so much bull in one post.
The reason why you don't just make a fast design and post it is probably the same reason you're looking for some ready made design.

I really cannot fathom your purpose - you're not here to learn, neither to teach, so I'll spare you from commenting any further on your posts.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline ambcorp2000Topic starter

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Re: MOSFET/IGBT based full bridge motor driver
« Reply #11 on: October 07, 2011, 12:30:47 AM »
Discrete components have dissappeared? You mean one can not buy a transistor, or a zener or a diode or a resistor? Soren is that what you gathered from my post? And all the info that I posted above explaining how/why all transistors are not born equal is not useful cos you tried to convince me that since I was light years away from being a professional and I should believe that evetything in a To-220 package is just a three legged creature? Why don't you look at your own postings above, do a word count and see how much of your own are educational?

However since you will not respond to my posts, for which I am actually thankful, I am actually inclined to think that the knowledge to word ratio might just improve  ;D

Offline maoxao

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Re: MOSFET/IGBT based full bridge motor driver
« Reply #12 on: October 08, 2011, 11:53:25 AM »
I think we discuss only technical here-

ambcorp- you should take out the "expert" thing- that is the only fault I see- if you are expert give more help-

soren-  your comments means no one talk like their mind- they should first think... what will soren think? Oh I am afraid this is not like by soren- soren if you have this problem please stop answering all question. Not only this one here...

I am new but I will talk what my mind think not what other member want me think- will try to teach and learn but my way not some other way-

Offline Soeren

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Re: MOSFET/IGBT based full bridge motor driver
« Reply #13 on: October 08, 2011, 06:11:49 PM »
I think we discuss only technical here-

ambcorp- you should take out the "expert" thing- that is the only fault I see- if you are expert give more help-

soren-  your comments means no one talk like their mind- they should first think... what will soren think? Oh I am afraid this is not like by soren- soren if you have this problem please stop answering all question. Not only this one here...
You (and a certain other) are the ones that seems to have a problem here and since we really haven't exactly seen a lot from either of you, excuse me for not taking you all too serious. I'm not saying you have a bad rep or nothing, just that you have no rep at all yet and I only take people serious when I know what makes them tick ;)


I am new but I will talk what my mind think not what other member want me think-
Hey, I'm a Dane and as such, I firmly believe in freedom of speech, which you apparently advocate here - just funny that you do it by trying to censor others  ;D
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

 


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