Please compare two fast mains transient protection circuits

[ocset]

Hi,
Which of the two Mains Transient protection circuits (attached) will  give the best mains transient protection…top or bottom?
There is also  a  Littelfuse surge protection device in the AC  line (not shown here), but it has 1100V of let-through.
(we don’t have much room on the PCB)

[madires]

I'm not an expert, but are there any reasons not to use simply a TVS for example?

[T3sl4co1l]

Be a bit surprised if either passes your toy "transient generator", let alone a real 61000-4-5 surge.

Tim

[ocset]

I'm not an expert, but are there any reasons not to use simply a TVS for example?

Thanks thats a good question.......we cannot use a TVS, because there are none  on the market that give enough protection at the 450V level, without also being triggered on high level UK mains.

TVS's unfortunately, as you know, dont conveniently clamp at a certain voltage, they rather start clmaping at a lower voltage, and then as the curerent in them rises, their clamp voltage also rises......eg a 440V TVS starts clamping at around 440V.. but when there's 2.7A flowing in it...it is clamping at 660V or so.............such a TVS would stray too far above the 450V level to be any good at protecting our 450V rated LED driver IC.

[M. András]

then if you know what the driver's operating current is, size the fuse correctly to trip if the tvs diodes start conduction.

[ocset]

Thanks, but we want to survive the transinet , and go on working, not trip the fuse.