Electronics > Projects, Designs, and Technical Stuff
Shielding ground - which side of my CM choke?
jrs45:
I have a project I'm working on that is powered by 24VDC via an external adapter. There is a CM choke isolating local board GND (and power) from the DC input wires.
I assume I should be connecting my shield to the local PCB ground, not on the other side of the CM choke (on the DC negative input)? Seems to be the way things are done but I wasn't sure, since on-board noise on the GND planes and whatnot might cause problems?
T3sl4co1l:
What shield?
Tim
coppercone2:
if you should float the shield by the impedance of the choke or ground the shield at a elevated impedance?
jrs45:
--- Quote from: T3sl4co1l on August 28, 2020, 01:16:45 am ---What shield?
Tim
--- End quote ---
The electrical shield - the enclosure box itself. I could connect it to the local PCB ground, or to the DC input's negative terminal (on the other side of the CM choke). Pretty sure the first is "what's done" but I wanted to check.
jrs45:
--- Quote from: coppercone2 on August 28, 2020, 02:49:45 am ---if you should float the shield by the impedance of the choke or ground the shield at a elevated impedance?
--- End quote ---
Something like that. The PCB has its own ground, and this is isolated from the DC input by a CM choke for conducted EMI purposes. For reducing radiated EMI, does the physical chassis shield go to the local PCB ground, or the DC input negative terminal (which is probably floating anyway, being fed from a switchmode power supply).
Perhaps since the negative DC input terminal is floating anyway, it doesn't matter? There is no earth present (or needed, no mains involved). Seems people connect it to the local PCB gnd but I wasn't sure if that was always the best case, or why.
The PCB is fairly noisy, lots of current being switched quickly, so I want to get it right.
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