No floating nodes
The schematic below was screen-shot from a LinkedIn group. I heard alarm bells go off in my head when I saw it (Figure 1).
Figure 1 A suggested application note diagram found in a LinkedIn group with a floating node between C4 and C5 that could lead to voltage breakdown.
Capacitors C4 and C5 are placed in series with each other so that their common node has no DC path to anywhere. When I worked on some spacecraft projects, this was absolutely a forbidden thing to do because any floating node like this could drift to an indeterminately high voltage and lead to voltage breakdown.
Even in an earthly milieu, this can be a problem. Imagine something being used or merely being transported or shipped in a thunderstorm environment. Dr. Frankenstein’s lightning bolts could do some real harm.
I have no idea why in the above schematic the series pair of C4 and C5 wasn’t simply made a single 0.5 pF capacitance.
The basic badness of letting something float has been looked at before in “Design precaution: Leave nothing floating”.
It looks like someone didn’t get the message.
John Dunn is an electronics consultant, and a graduate of The Polytechnic Institute of Brooklyn (BSEE) and of New York University (MSEE).
Related Content
Design precaution: Leave nothing floating
Floats like a butterfly, stings like a bee
The ground illusion: Don’t let it come back to get you
Electrical noise and mitigation – Part 2: Ground loops, noise transmission and shielding
<!–
VIDEO AD
–><!–
div-gpt-ad-inread
–>
googletag.cmd.push(function() { googletag.display(‘div-gpt-ad-native’); });
–>
The post No floating nodes appeared first on EDN.
