EMC/EMI filter question

[john swift]

the EMI filter could be like this



the choke has a low impedance at the mains frequency but
a high impedance to the high frequency noise your trying to block

the capacitors are just the opposite
a high impedance at mains frequency and a low impedance to high frequency noise

so the mains supply passes through uneffected but any high frequency noise between live & neutral are short circuited by capacitors C1 & C2

any noise between the supply lines ( live & neutral) and earth will pass through capacitors C3 & C4 to be grounded

the filter may be potted in a metal enclosure

if VDR's are added to provide transient voltage protection like this



you need a fuse in the live connection as VDR's very often go short circuit when they fail


John