SMPS Gnd, Chassis-Gnd, and Layer Stack

[gearheadgene]

On the line-side of SMPS (non-isolated), are all the circuit-common connections to chassis-ground? Or are the protection devices connected to chassis-ground, but the rest of the circuit uses a floating common. Maybe it makes sense to do it this way - I just want to be certain, and safe, and within the confines of UL, for example.

On the secondary (isolated) side, the circuit-common is also another 'ground'. At some point it eventually may connect to chassis ground through whatever circuitry is attached to it (an amplifier, for example). The option for a floating supply is easy if the circuit common remains floating. It can be easily grounded to Earth, if desired, just like a lab supply. Are there any safety concerns with this arrangement?

On the PCB design, 2-layer seems appropriate for SMPS design. But, is 4-layer a better choice? I believe with 2-layer, it's much easy to physically steer the currents using traces. With 4-layer the opportunity for using power and/or ground plane is possible. But now steering the currents is less deterministic.

regards,

gene

[marce]

You can use 2 or 4 layers depending on the design.
EMC Information Centre - The EMC Journal (Free in the UK)
there is a series of articles regarding EMC problems with SMPS designs on the above site by Keith Armstrong, I would reccomend reading it to get an insight into some problems you are going to face.
Steering currents on any PCB is only reccomended if you know what you are doing, and on SMPS's it can be critical. I have seen many imported SMPS's squeal all over the spectrum when checking EMC.
The rest would require a schematic to comment on.