We are designing an appliance with integrated power monitoring and I would appreciate some suggestions for meeting EMC and safety requirements (EN55014 and IEC60335-1).
I have read your AN-1332 and admire the PCB-integrated stitching capacitor: it is low inductance and inexpensive, as long as you are OK with a 4-layer board. However, I'm not convinced I can use it in my application. I don't have access to the IEC6052-31 standard being designed to in the application note, but from the application note I gather that a 0.4mm separation is sufficient insulation thickness for energy meters. In my reading of IEC60335-1, which applies to appliances, the insulation thickness between AC mains and the low voltage side (reinforced insulation) must be >= 2mm. That requirement cannot be satisfied on a conventional 1.6mm thick 2-layer PCB, much less a 4-layer one. So the two ground planes cannot overlap to create a capacitor.
Some options I am considering are:
- Using a discrete Y2-rated stitching capacitor. My dilemma is that SMT capacitors are not that long so I question whether they meet clearance requirements, but radial through-hole capacitors probably don't have the kind of high frequency performance needed to suppress those 383 MHz and 766 MHz emissions peaks.
- Putting the whole thing in a metal box. Right now it is in plastic.
- Both of the above.
Do you have any recommendations based on tests you have run with the IC?