Electronics > Electronics

New H-bridge for my Robotic Car!

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--- Quote from: waltr on March 07, 2013, 09:03:40 PM ---Why did you connect the A and B grounds on the ACUM isolator?

--- End quote ---

You kinda freaked me out for a moment, that´s not really A and B. It´s input circuit ground and one isolated driver ground.
The project is battery powered, the isolation is needed for the high side, but you get the same isolator - mosfet driver for
the low side also because you want to kinda match the propagation delay ;-)
The low side isolator - driver, is only used as a driver for the mosfet.
And to be sure that I help you with your question, note that the drivers are isolated from each other also.
You have 3 grounds, 1 ground for each driver (resulting in 2 grounds) and 1 ground for the input circuit ;-)

Opps... I meant the connect between GND1 (pin 4) and GND_B (pin 9).
Is there only one Battery?
It does make sense to connect these GND pins in that case.
If you are using two batteries, one for the controller logic and one for the motors
 then not connecting the GNDs could be better to keep the motor switching noise isolated from the logic.

Do you have the option of cutting this trace?


--- Quote from: waltr on March 08, 2013, 07:10:51 PM ---Do you have the option of cutting this trace?

--- End quote ---

Hmmm, yeeeaahhh eeehhh... yes you need to make two cuts and it´s possible but well,
there is the idea of placing common mode chokes rather than more batteries...

Having two batteries isn´t really what I expect to have in my project, get´s things messy with charging.
I really prefer the "one battery to rule them all" method, which by the way is a problem now. I am
thinking of 3s lipos @ 5Ah (at least 5Ah) but yeah that´s another subject so...

So, yes, you can separate the grounds no problem, but generally, I don´t like the idea. I am
using high noise reject ration regulators, chokes and many other stuff.
But even with the previous designs, I really hadn´t any problem with noise problems so...

In short I really want to avoid, even the idea of a second battery. Still I exclude nothing.
But generally that´s the idea. :-P

Best Regards,
Lefteris, Greece

BTW, I am testing the s*cker, so I should will have results soon :-)

Isn't the whole point of isolator components that you isolate the grounds? Else you might as well just use a MOSFET or something.


--- Quote from: jwatte on March 09, 2013, 07:53:34 PM ---Isn't the whole point of isolator components that you isolate the grounds? Else you might as well just use a MOSFET or something.

--- End quote ---

That was what I was thinking when I saw the grounds connected.

I now see that the ADUM4223 was used to have a 'floating' high side gate driver so that the OP could use four N channel MOSFETs.
This should work and only need one battery source.

But, even with one battery the trace between the grounds could be (and may need to be) cut. The power and ground wires for the
H-bridges should be directly connected to the battery and like wise, the power and grounds for the logic should also go directly to
the battery. This is called a 'star' connection which controls the current flow path for each load.
Then the ADUM4223's input side (GND1) only connects to the logic and the GND_B to the H-bridge. The two ground are common
only at the battery.


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