Fuse selection for Flyback application under Surge conditions

[Bjtpower_magic]

The voltage on the MOV will not reach 661V, because the capacitor, your bulk input electrolytic, will stop the voltage from getting that high...you must have a bulk electrolytic input cap, because you say you're at 70w and non-PFC'd.

How bulk capacitor will help when it is fully charged during surge.

It doesnt need surge components, because the bulk cap clamps the voltage down low.........it shows a 1kv 1.2/50us transient, and the voltage stays below 450V at your flyback....no MOV needed there.

How? i have 100uF/450V after bridge rectifier.

 

[zenerbjt]

OK , so put the 100uF in the simulation of post #12, which shows a 1kV 1.2/50us transient into a 2R mains, and see how high the voltage goes in the flyback. It will be less than 450V.

Yes, The bulk cap will be at mains peak voltage during the surge, because most surges happen at mains peak...and the Bulk cap will have some 339V on it......and its voltage doesnt rise up much more during the transient...run the sim of #12 and see it for yourself.

--- Updated Sep 22, 2020 ---

Some time ago on edaboard there was a discussion on how bulk el caps can limit mains transients...but i cant find the thred now

https://www.edaboard.com/threads/handling-mains-transients-with-bigger-post-pfc-electrolytics-in-offline-smps.365666/

..its thread number 352771, and its actually Synqor who profess it.
But i cant find edaboard thread 352771.

 

[Bjtpower_magic]

Hi,
What is Open circuit voltage and short circuit current in surge?

How it is associated with test setup of surge?
Can someone explain test setup with explanation?

 

[FvM]

It's discussed in the link in post #6. Open circuit voltage is the specified surge level, short circuit current is given by 2 ohm network impedance.