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what is the benefit of connecting DC ground terminal to the Earth in AC to DC converter?

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closed as too broad by Marcus Müller, Olin Lathrop, winny, laptop2d, mkeith Jun 8 '18 at 22:58

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    \$\begingroup\$ If you want the floating feature you simply don't ground. You ground it for safety and/or to have a common ground with some other equipment if required. \$\endgroup\$ – Eugene Sh. Jun 7 '18 at 14:58
  • \$\begingroup\$ i just want to know the benefit as stated in the questions , so all of that is just a protection from being shocked if the line wire touch the ground \$\endgroup\$ – isam Jun 7 '18 at 15:11
  • \$\begingroup\$ "in some circuits": This is too broad. In engineering, we do things to achieve a certain goal. I'd recommend picking one example, and asking why. Maybe you can research reasons for that one purpose and discuss these already in your question? Until you do that, I think the appropriate reaction to your question for now is considering it too broad to be answerable. \$\endgroup\$ – Marcus Müller Jun 7 '18 at 15:12
  • \$\begingroup\$ @MarcusMüller i edited the question \$\endgroup\$ – isam Jun 7 '18 at 15:16
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    \$\begingroup\$ You broadened it even further. \$\endgroup\$ – Marcus Müller Jun 7 '18 at 15:58
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One of the common reasons is to reduce output common mode noise. On an unearthed SMPS, the primary winding is capacitively coupled to the secondary winding by several hundred pF in some cases and this means that although the DC differential voltage might be pure DC with low ripple, both DC terminals can have significant common-mode noise from the primary.

Earthing one leg of the DC output can dramatically reduce this effect. When an SMPS is used that doesn't require an earth, what is normally done to remove output common-mode switching noise is to use a Y rated capacitor of about 1 nF between the output winding and the rectified DC bus on the primary however, it isn't as effective as earthing the DC output.

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