Universal Mains Filter

Published:2011/8/11 21:35:00 Author:Amy From:SeekIC

Ton Giesberts

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.



Be careful that you don’t use a vertical version of the coil. These appear to be pin-compatible, but they have different connections. They would cause a severe short-circuit on this PCB! For this reason we haven’t included them in the table (they have a K instead of an A in their order code).

This filter is suitable for use up to 3.6 A (a good 800 VA). In practice there should be no need to use different values for the capacitors. You should make sure that you obtain the correct lead spacing and that they’re X2 types. For the 100 nF capacitors provision is only made for a lead spacing of 15 mm (as these are the most common). For the 10 nF capacitors you can use either 10 or 15 mm types.

A final warning: always take great care when working with mains voltages!

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