Mains powered SMPS....earthing and diff. mode EMC?

[treez]

Hello,

For any given transformer isolated 230VAC mains powered SMPS, how do you know how to manage the Earth grounding configuration?, ……


…..and how do you know whether or not Earth should be wired to the SMPS at all?……………..
…and how do you know whether the chassis should be connected to earth ground or not?
[“chassis” being the chassis of the product in which the smps resides (ie the thing the smps powers)…….and/or the chassis of the smps if its metal]

And should the output return be………..
1….directly connected to earth ground?
2….Capacitively connected to the chassis and earth ground?

If earth ground is brought into an smps, should it always be connected to the chassis of the product in which the smps resisdes (the product which the smps powers)?

The powerint.com 20007 Datebook and design guide……………
**broken link removed**

…….is one of the worlds best references on smps, …….inside this databook, there are many different earth configurations, but its not clear when you should use which one.

Eg inside the databook…….

Page 2-130 has an AC split y cap connected to earth at the centre……and the output is connected to earth ground.
Page 2-50 has only a y cap from primary to secondary, and no earth ground at all.
Page 2-185 has no earth ground brought to the smps.
Page 3-18 has input neutral and output common connected.
Page 3-25 has Earth connected to the centre of the two y caps connecting primary and secondary…..and this point is also chassis connected.
Page 3-222 has earth connected to output common.
Page 3-292 has output return capacitively connected to chassis, but there is no earth connection to the chassis


Which earthing configuration should you use, when should you use it, and why?

 

[chuckey]

If you start hanging capacitors anywhere between the mains input connector and any point downstream of the inverter transformer then you must run a mains earth to the output line, This is so if the capacitor goes short circuit, the output circuit does not become live . Some really cheapo SMPSs are mains in (L&N) with serial L and C between L&N. With the internal screen connected to one of the output terminals.
The thing to do is to arrange it so your SMPS does not radiate noise down eithe input or output lines as cheaply as possible, so trying not to have to put in an earth terminal and mains filter caps connected to it.
Frank