Page 12 of the following shows a 240W offline PSU schematic. The MOV is placed after the input LC filter.
Surely you agree that this is totally wrong?, and the MOV should appear after the input fuse?
After all, the input LC filter will ring up to a high voltage whenever the mains is applied at the instant of mains peak, and the MOV will end up quenching this ringing voltage…which will reduce its lifetime unnecessarily.
A MOV is simply to quench line overvoltage transients.
If it is required to damp down input LC filter overvoltage transients caused by ringing at application of mains at the instant of mains peak, then the filter inductors should be placed after the diode bridge and should feature diodes across them (cathode on input connector side)
Alternatively a TVS should be used following the mains input filer, though this is not recommended.
Please see page 12..
https://www.onsemi.com/pub_link/Collateral/DN05067-D.PDF
The schematic of page 12 is simulated here to show the overvoltage ring that the MOV would have to quench every time the SMPS is plugged in to the mains...
Surely you agree that this is totally wrong?, and the MOV should appear after the input fuse?
After all, the input LC filter will ring up to a high voltage whenever the mains is applied at the instant of mains peak, and the MOV will end up quenching this ringing voltage…which will reduce its lifetime unnecessarily.
A MOV is simply to quench line overvoltage transients.
If it is required to damp down input LC filter overvoltage transients caused by ringing at application of mains at the instant of mains peak, then the filter inductors should be placed after the diode bridge and should feature diodes across them (cathode on input connector side)
Alternatively a TVS should be used following the mains input filer, though this is not recommended.
Please see page 12..
https://www.onsemi.com/pub_link/Collateral/DN05067-D.PDF
The schematic of page 12 is simulated here to show the overvoltage ring that the MOV would have to quench every time the SMPS is plugged in to the mains...