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I'm trying to design the isolated SMPS circuit. I'm a newbie on power electronics and I'm using a circuit design tool to design SMPS. I have confusion about grounding and earthing. My system will have a PE(Protective Earth) connection but I'm not clear to where I must connect it?

The auto-created circuit designed by the tool is below. As schema shows that Y1/Y2 safety capacitor is connected through the rectifier ground (I called it Primary Ground) enter image description here

I got and SMPS and investigated the circuit. They connected safety capacitors to PE not to Primary Ground. And they made connection between all grounds and PE by other safety capacitors. enter image description here

Which way to I use? As I guess the auto-created circuit for Class 2 applications. My design will be Class 1 (PE connected) so I must design something like the second one. I need expert advice about this grounding issue.

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  • \$\begingroup\$ The capacitors are there for reasons of EMI suppression and that EMI will be heavily influenced by your design. \$\endgroup\$
    – Andy aka
    Commented Aug 4, 2020 at 9:28
  • \$\begingroup\$ I agreed. But I'm not clear about connecting them to either PE or Primary Ground. (the section that before rectifier circuit) Doesn't it change anything? \$\endgroup\$
    – İsmail Fatih ILTAR
    Commented Aug 4, 2020 at 10:38
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    \$\begingroup\$ What you call primary ground is not earth; it's just a reference node name and not real earth or PE. Don't confuse the two. \$\endgroup\$
    – Andy aka
    Commented Aug 4, 2020 at 10:40
  • \$\begingroup\$ Primary Ground is a kind of Ground that used for Pwm controller, MOSFET, optocoupler, and negative side of the input bulk capacitor. A point that a confused is I must or musn't connect Y1/Y2 safety capacitor(Line to earth/ Neutral to earth) to PE or direct to the Primary Ground. Auto-created circuit says that I must connect it to primary ground but real smps circuit says that I must connect it to PE. \$\endgroup\$
    – İsmail Fatih ILTAR
    Commented Aug 4, 2020 at 10:56
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    \$\begingroup\$ Then "auto-created-circuit" is wrong. \$\endgroup\$
    – Andy aka
    Commented Aug 4, 2020 at 11:06

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