Universal Mains Filter

There are plenty of mains filters available, with or without sockets, with or without a switch, etc. In any case, this filter is very versatile as far as the maximum working current is concerned. It so happens that the footprint of the coil remains the same for different currents. Depending on the required specification, you can use a specific coil (which the manufacturer calls a ‘Current-Compensated Ring Core Double Choke’). The table below lists a suitable range of coils made by Epcos. When we designed the PCB we chose the smallest size that still gave a wide selection of maximum currents.

Resistors:
R1,R2 = 470kOhm 
Capacitors:
C1,C2 = 10nF 275 VAC X2, lead pitch 10 or 15mm
C3,C4 = 100 n/275 VAC X2, lead pitch 15mm
Inductors:
L1 = B82721-A2401-N20, Epcos (Farnell 976-477)
Miscellaneous:
K1 = 3-way PCB terminal block, lead pitch 7.5mm
K2 = 2-way PCB terminal block, lead pitch 7.5mm