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Back to Back Schottky Diodes

Fish4Fun

So long, and Thanks for all the Fish!
Aug 27, 2013
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I am designing//building a "heavy duty" amplifier for a sensored BLDC motor (referenced here https://www.electronicspoint.com/forums/threads/sensored-bldc-motor-question.292730/ ) and am trying to decide how "isolated" it needs to be from the control system ... So, I have been reading up on analog/digital ground theories and practices ... "ground bounce" etc, etc. I ran across a Ti white paper ( http://www.ti.com/lit/an/slyt499/slyt499.pdf ) that suggests using "Back to Back Schottky Diodes" between the Digital Ground Plane and the Analog Ground Plane ....

The paper discusses the reasoning and suggested placement of said Schottky Diodes, but fails to show schematically what is meant by "Back to Back" .... Being dyslexic, I needed a picture, so that sent me Googling .... which was not nearly as helpful as I might have hoped...

upload_2020-4-3_7-13-47.png


upload_2020-4-3_7-14-13.png

While Optical Isolation will probably be the method I actually employ, I would like to get this concept of Back to Back Schottky Diodes straight in my head (and forever stored here ;-) ) for future reference.

Thanks in Advance!

Fish
 

bertus

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Nov 8, 2019
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Hello,

The upper schematic shows anti-parallel diodes.
The voltage differende between the two gounds will be max 1 diode voltage drop.
The lower schematic has the diodes back to back.
There will never flow any current, until the reverse breakdown voltage of the diode.

Bertus
 

Fish4Fun

So long, and Thanks for all the Fish!
Aug 27, 2013
471
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@ bertus

Thanks ... I couldn't see how figure 2 could do anything useful; however, I have thought that about several things over the years and been wrong. If the Ti white paper had simply used the phrase "anti-parallel diodes" then I would have known exactly what they meant ... "Back to Back" did not carry the same connotation to my dyslexic way of thinking.

Fish
 
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