Earthing & EMI filter.
Posted by: sankalp.gitaje
on
Hi,
We are designing DC to dc converter using DPA switch having input voltage 20 to 60Vdc, output 24V, 50W. As we have metal enclosure it needs earthing for safety. Please suggest emi emc filter consideration for same or any application note available.
How to calculate input bulk capacitor value as input is DC voltage?
Normally the EMI earth should be connected to the output return, but it is decided by your customer and applications, so you have to discuss the earth connection with your customer.
For the EMI filter, you can try a PI filter. For your application, I guess forward topology will be used . PLS use the DI31 as a reference :http://www.powerint.com/sites/default/files/PDFFiles/di31.pdf. In the DI131, the capacitor before the input inductor is half of the capacitors after the input inductor.
For the input capacitor calaculation: The capacitance should be calculated based on the voltage ripple. C=(Io*Np/ns-Po/effi/Vin)*DT/Vripple. The calaculation assues the current through the input inductor is DC, and neglect the current ripple of output inductor.
Regards