Breaking inductive current in EMC filter

[triacmov]

Hello,

My company has had various incidences of (1KW) SMPS's blowing up at the point of switch-on or switch-off.

For switch-off blow-ups, I am personally wondering if this is due to the breaking of the inductive current in the EMC filter elements at switch off. -eg the common mode choke's magnetising inductance.

-They have MOV's at the input but only on the line side of the EMC filter.

In short, there is no path for the EMC filter's inductive current at switch-off except through the MOV and also through the high-value bleed resistor on the output of the Boost PFC......This is not a good path for this current.

-I suspect that the back EMF at switch off is ramming the inductive current through the PFC Boosts MOSFET even though its off.

Any ideas on handling the breaking of inductive current in EMC filters at switch-off would leave me most ingratitudinous.

 

[DHambley]

Sounds like someone at your company needs to calculate the inductive energy and design in a MOV/snubber/whatever to absorb this spike so that the PFC transistor doesn't get this surge.