Simple H-bridge configuration.

Other Hardware Motors, Mechanics, Power and CNC
1

Hello, it's been awhile since my last post, and now I'm onto a new project, sorta. Some background...I built a 2-axis solar-tracking system that uses a tarp motor for rotation, with a LRA of 50 amps @ 12VDC, and a linear actuator with a LRA of 25 amps, also at 12VDC. The whole thing is controlled with a Mega plugged into a PCB that I made to make it easy to connect everything. That and a cheap Chinese H-bridge fit neatly into a metal box, and after much trial and tribulation, everything works really, really well, which leads to the next phase of my learning curve. A programming error led to a burned out H-bridge, and being the incurable tinkerer that I am, I took it apart to see what they used for components: The switches are 8, International Rectifier IRFB3077 MOSFETS, and for flyback diodes, it appears that they are using Vishay Transient voltage suppressors, although I can't tell which variant at this point. There is a lot of other stuff on the board, obviously, but it does a lot of things I don't use, so I don't know what is necessary and what is not for my application.

Enough rambling. My question is, how hard would it be, using the same FETs and suppressors, and using 4 of the PWM pins on the Mega (4,5,6, and 7, to be exact), to build a workable 2-channel H-bridge? I would write the movement functions in the program to avoid shoot-through (I think they call it) situations. I'd also connect the FETs to much heavier copper bus bars and heatsinks, just for my own peace of mind.

Any advice or thoughts would be appreciated. I am able to make double-sided PCBs, and surface mount resistors and caps are not a problem to work with, although I have not tried anything SM more complex than the 2-point stuff.

Thanks in advance.

Oh, I forgot to add that I could spare 8 PWM pins on the Mega, one for each FET, if that would simplify things? (Or not....)

2

JohnDeere630:
Hello, it's been awhile since my last post, and now I'm onto a new project, sorta.

Some background...I built a 2-axis solar-tracking system that uses a tarp motor for rotation, with a LRA of 50 amps @ 12VDC, and a linear actuator with a LRA of 25 amps, also at 12VDC.

The whole thing is controlled with a Mega plugged into a PCB that I made to make it easy to connect everything.
That and a cheap Chinese H-bridge fit neatly into a metal box, and after much trial and tribulation, everything works really, really well, which leads to the next phase of my learning curve.

A programming error led to a burned out H-bridge, and being the incurable tinkerer that I am, I took it apart to see what they used for components:

The switches are 8, International Rectifier IRFB3077 MOSFETS, and for flyback diodes, it appears that they are using Vishay Transient voltage suppressors, although I can't tell which variant at this point.

There is a lot of other stuff on the board, obviously, but it does a lot of things I don't use, so I don't know what is necessary and what is not for my application.

Enough rambling.

My question is, how hard would it be, using the same FETs and suppressors, and using 4 of the PWM pins on the Mega (4,5,6, and 7, to be exact), to build a workable 2-channel H-bridge?

I would write the movement functions in the program to avoid shoot-through (I think they call it) situations.
I'd also connect the FETs to much heavier copper bus bars and heatsinks, just for my own peace of mind.

Any advice or thoughts would be appreciated.
I am able to make double-sided PCBs, and surface mount resistors and caps are not a problem to work with, although I have not tried anything SM more complex than the 2-point stuff.

Thanks in advance.

Oh, I forgot to add that I could spare 8 PWM pins on the Mega, one for each FET, if that would simplify things? (Or not....)

Sorry, I had to spread it out to see the relevant points.
Tom... :slight_smile:

3

Hi,
Your Driver.
driver1.jpg

It has more than just MOSFETs and voltage suppressors, it has some contolling ICs to help with the H-Bridge drive probably including shoot-through.

Can you please tell us your electronics, programming, Arduino, hardware experience?

Thanks.. Tom.. :slight_smile:

4

Hi Tom,
Yes, that is the driver. There is some different logic chips on it that I assume prevent shoot-through, as well as over-current protection, probably other things as well. The documentation is pretty sparse.

Regarding my experience level, it is not super high. I am currently attempting to wade through Practical Electronics for Inventors by Paul Scherz. I am about at the stage where I know the difference between a FET and a BJT, an NPN and PNP, etc. I just learned what inductors do and how they do it, but have no idea how that property is useful in a circuit.

I am a fair hand with a soldering iron, routinely soldering SMT resistors, leds and caps. I also make my own PCBs, although in this instance, it needs much heavier conductors than I can achieve on a regular PCB.

Regarding programming, I wrote the program for the mega that controls everything, about 2500 lines, so I'd consider myself an intermediate-level arduino C programmer.

I can follow a schematic well enough to build a circuit, but lack the engineering knowledge to design something like this.

I did just design and build a circuit around a nano, a PIR sensor and an op-amp that senses a cat's presence and makes a scary noise to keep it out of my wife's plants in the sunroom..LOL

Anyway, I am trying to ascertain if the PWM signal from an arduino pin can directly control these FETs, or if there must be an intermediary transistor. I think (could be wrong) that I can do whatever logic is needed on the mega board to avoid shoot-through. As for current limiting, I have no idea how to do that, although these FETs are good for around 150 amps, with proper cooling, and that is way more than either of these motors would ever draw, so maybe a fuse would be sufficient?

Lots to learn, but the FETS and mega are reasonably cheap, and it wouldn't be the first time I let the magic smoke out of some electronic parts......

Thanks for replying!

5

Yes, there must be an intermediary transistor, in fact many of them:

  1. The high-side switches require a voltage equivalent to the high side voltage - you can't switch a transistor at 12V with a control signal that only goes up to 5V

  2. You must switch the MOSFETs fast to avoid operating in their high-resistance linear mode. 20A gate drive is not uncommon. A thousand times more than the Arduino pins can deliver.

  3. Shoot-through, as discussed above. This also develops into asymmetric operation: switch-off faster than the switch-on.

And a bunch more things...

6

MorganS:
Yes, there must be an intermediary transistor, in fact many of them:

  1. The high-side switches require a voltage equivalent to the high side voltage - you can't switch a transistor at 12V with a control signal that only goes up to 5V

  2. You must switch the MOSFETs fast to avoid operating in their high-resistance linear mode. 20A gate drive is not uncommon. A thousand times more than the Arduino pins can deliver.

  3. Shoot-through, as discussed above. This also develops into asymmetric operation: switch-off faster than the switch-on.

And a bunch more things...

Hi Morgan,
That would explain the 4, IR2103S gate drivers, and there are 3 chips that I assume are some form of opto-couplers. The only markings on them are the numbers 2631 1619T1. They are an 8-pin chip. Any logic must be provided either by the drivers or the couplers, since the only other chip of note is what appears to be a heavy voltage regulator, marked LM2576.

I feel foolish, as I now recall reading that fet gate voltages are always expressed in terms of the source voltage. Sorry about that. I also now recall reading in a forum post that someone burnt up some fets because they were switched on too slow.

As I said, there is a lot to learn....but it is certainly interesting.

7

and for flyback diodes, it appears that they are using Vishay Transient voltage suppressors

No, those are transient voltage suppressors used to suppress voltage transients :slight_smile:

A MOSFET H-bridge doesn't need extra free-wheel diodes as every MOSFET contains a body diode.

The datasheet for the HIP4081A MOSFET H-bridge driver has quite a bit of stuff about
driving MOSFET H-bridges, a good starting point.

Note that at these high voltage and power levels H-bridge design gets tricky as any fault
condition (sometimes only for very short periods of microseconds) can lead to catastrophic
failure. If you are going to experiment with making H-bridges start with much lower currents and
gain confidence first.

With high current circuitry its important to wear eye-protection as a failed MOSFET can explode,
and accidental shorts spray metal vapour and drops of molten metal out. The kind of batteries that
drive a steady 20A load may deliver 100's of amps to a short-circuit. Fusing is important - its
primary function is to fail before the wiring overheats/burns up.

8

MarkT:
No, those are transient voltage suppressors used to suppress voltage transients :slight_smile:

A MOSFET H-bridge doesn't need extra free-wheel diodes as every MOSFET contains a body diode.

Thanks Mark, that I did not know. Makes sense in retrospect, though. I am currently looking at how those gate drivers are set up. It would be so nice to have a schematic, since it's pretty hard to tell what goes where. There is an inductor on the board too, and I would guess that it has something to do with current limiting? Since inductors resist changes in current, as I understand it, I can't imagine what else it does. I could, however, be completely wrong. It wouldn't be the first time.

9

The inductor is part of a DC-DC converter I think, looks like an LM2596 in fact, probably generating the 12V
for the drivers. The module description says its motor voltage range is limited to 12V to 48V range, suggesting
a buck converter down from this to get the driver's 12V rail (they might be using 10V anyway, that's fine).

10

MarkT:
A MOSFET H-bridge doesn't need extra free-wheel diodes as every MOSFET contains a body diode.

Worth pointing out what MarkT also said in a thread I started here:

MarkT:
With an H-bridge each MOSFET's [body] diode acts as a free-wheel for the other MOSFET in that leg of
the bridge.