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Author Topic: Looking to design/ build a pair of H Bridges  (Read 1833 times)
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I'm going to start off by saying I'm a mechanical engineer, so I might need things explained to me as they would be to a child.

I am looking to build two H bridge motor controllers to control both direction and speed for 2 motors with a stall current of 14.5 A, although I expect to be running them much more in the 2-5 A range. I know what an H bridge is and how to operate one, but I am trying to avoid spending a huge grip on something like one of those $50-60 Pololu Dual motor controllers or a $70 Sabertooth Dual motor driver. I also want to learn some new stuff about electrical engineering instead of just buying something.

I understand how an H bridge is supposed to work, especially in the context of a motor with regard to direction, braking, free running, but I have discovered through laughably unsuccessful testing that Darlington Power Transistors are probably the wrong way to go. I'm looking into MOSFETs, of which I know nothing except that they are easier to break (?), but they seem to be able to handle greater currents (despite BJT's being the so called "current driven transistors" and FETs being the "voltage driven transistors"). Anywho, I am looking to control my robot with an Arduino's Digital I/O and PWM pins. My concern is that while looking at datasheets for power MOSFETs on Jameco.com is that all of the threshold voltages show a range of 2-4V with 2.9 typical. Would I kill one of these things with a 5V (or 4.5-4.9V what ever the range is) Arduino signal? Is there a way to bring the Voltage down? I wouldn't really have a clue since the extent of my electrical circuit analysis pretty much stops at analyzing ideal OP Amp circuits and normal, useless, KCL KVL RCL circuit analysis. Does anyone know of any good (free) online guides or resources I could look into for designing moderately high current H bridges, or at least something on using MOSFETs are switches? Any help would be graciously appreciated.

Don't worry so much about the multi direction and speed control part, I'm just trying to figure out what signals to send to a MOSFET and how to condition them from an Arduino.
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At 14-15amp range, you need fairly beefy mosfets and you will need to use a mosfet gate driver for those things at moderate switching frequencies (1k or up).

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the land of sun+snow
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Just to get some background, you might look through 6 or 15 of the sites linked here,

http://www.google.com/search?num=10&hl=en&site=imghp&tbm=isch&source=hp&biw=994&bih=833&q=h-bridge
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At 14-15amp range, you need fairly beefy mosfets and you will need to use a mosfet gate driver for those things at moderate switching frequencies (1k or up).


Why so high of frequencies? I noticed the Pololu and Sabertooth boards mentioned going up to ridiculously high PWM frequencies over 20kHz so you can avoid a high pitched whine, but is the Arduino standard ~500Hz PWM frequency insubstantial? Also I am looking at beefy MOSFETs, like this onehttps://www.jameco.com/Jameco/Products/ProdDS/210542.pdf. Looking at the maximum rating on the drain, 72A peak, 18A continuous I should be fine right?

Just to get some background, you might look through 6 or 15 of the sites linked here,

http://www.google.com/search?num=10&hl=en&site=imghp&tbm=isch&source=hp&biw=994&bih=833&q=h-bridge
I know how to Google lol, and I know what an H bridge is. My questions are more about using MOSFETs. Yes I Googled that and I can't find any good resources on circuit designing or component selection for MOSFETS either. That's why I'm asking here is someone can either explain this kind of stuff or knows of any good resources.
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the land of sun+snow
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someone can either explain this kind of stuff or knows of any good resources.

If you actually will look at those sites, you will find 100s of them are describing the
design considerations of BJT or MOSFET, or comparing both. They're not just
printing diagrams.

Honestly, people tend to think this stuff is trivial, and can be explained in a sentence or
two, but with h-bridges in the 15A range, you have no idea what you're getting into.
Do some legwork.
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For a homemade H Bridge of that calibre, you could do it with 2x SPDT relays. If you need PWM control, you need 1 MOSFET between the relays and power source.
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Honestly, people tend to think this stuff is trivial, and can be explained in a sentence or
two, but with h-bridges in the 15A range, you have no idea what you're getting into.

You would do well to heed this advice. Designing an h-bridge that works properly and doesn't self-destruct after you get past about 5 amps or so of current-capability gets difficult quickly. If your goal is to learn how to design and build such an h-bridge, and money isn't an issue, then go for it; you will learn a lot. If, however, your goal is to implement an h-bridge for some other project, you will probably find it cheaper to just purchase such an h-bridge that uses a proven design. Otherwise, in testing/experimenting with building your h-bridge, you may find yourself blowing expensive MOSFETs left and right - ultimately spending more money than if you had bought a properly-sized h-bridge in the first place...
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the land of sun+snow
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You would do well to heed this advice.

Wow, someone actually agreed with me this week! LOL.
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That's why I'm asking here is someone can either explain this kind of stuff or knows of any good resources.

below is some quick reading on DIY H-bridges. ebay has some affordable h-bridges available.

http://arduino.cc/forum/index.php?topic=53425.0

http://www.ebay.com/itm/43A-DC-Motor-Driver-Drive-Module-H-Bridge-PWM-Contro-For-Robot-Smart-Car-Arduino-/300818612987?pt=LH_DefaultDomain_0&hash=item460a2fc2fb

http://www.ebay.com/itm/30A-H-bridge-Coreless-Motor-Driver-Forward-Reversion-Brake-For-Smart-Car-Arduino-/180983568079?pt=LH_DefaultDomain_0&hash=item2a237616cf

http://www.ebay.com/itm/Dual-H-Bridge-Optoisolate-ATMEL-ATTINY-2313-based-Motor-driver-Arduino-PIC-/271028808736?pt=LH_DefaultDomain_0&hash=item3f1a936c20

http://www.ebay.com/itm/50A-Single-H-bridge-Motor-Driver-Module-PID-for-Arduino-Intelligent-Car-Robotic-/230888425765?pt=LH_DefaultDomain_0&hash=item35c205c925

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I love you.

Also how did you find these on ebay? When I search H bridge on ebay all I get was a bunch of garbage and L298N's. Thank you so much though!
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At 14-15amp range, you need fairly beefy mosfets and you will need to use a mosfet gate driver for those things at moderate switching frequencies (1k or up).



Large motors have a lot of inductance. Running the PWM at 1 KHz will make the motors absorb most of the power.

Probably 30 to 60 Hz would be a better range for a large motor.
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Looking at the maximum rating on the drain, 72A peak, 18A continuous I should be fine right?

Those ratings are typically for pulsed current (5us for example) into a resistive load, and with the case at 25c.

So I typically derate them 50% for my applications. For 15amp current, I use a 30amp (continuous) mosfet.
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These look like a fairly decent design. They know enough to place a large reservoir cap across the battery
lines [presumed location]. zoomkat, have you actually ever used any of these things yourself?

http://www.ebay.com/itm/30A-H-bridge-Coreless-Motor-Driver-Forward-Reversion-Brake-For-Smart-Car-Arduino-/180983568079?pt=LH_DefaultDomain_0&hash=item2a237616cf

I do like it how so many CN companies include Arduino in the product title even though the thingies have
nothing at all whatsoever to do with Arduino.

You do appear to need 2 different PWM signals to the board, and what are the parameters of the current
and voltage signal out? Unfortunately, they rarely seem to have much documentation.
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V +                Power Input +
GND             Power Input -
EN                 Driver Enable, high enable, low off
RPWM          Forward PWM input, high active
LPWM          Reverse PWM input, active high
CT                 Current signal output,analog signal
VT                 Voltage signal output, analog signal
« Last Edit: December 05, 2012, 01:28:22 pm by oric_dan(333) » Logged

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A discrete h-bridge is fairly difficult to design, primarily to get it to switch fast and to allow for the appropriate dead time.

If you are starting now, I would recommend that you look into h-bridge drivers (high/low-side drivers). They come in many different shapes, depending on your needs.

Generally, you need to decide if you want to have braking / motor hold; if you want to be able to drive high/low sides separately; if you allow enable signaling or not; your desired voltage ratings and if you want under/over voltage protection, etc.

Many firms offer such chips and they are generally easy to use. IRF, Fairchild and On would be good starting points.
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You would do well to heed this advice.

Wow, someone actually agreed with me this week! LOL.
Well add me to your list. Playing about with this sort of current is not trivial.
One thing that it is hard to get over to beginners is that electronics do not scale up easly.
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