Overvoltage when bayonet connector LED bulb is plugged in to live mains?

[FvM]

Ive added the wiring inductance, and the RC damper

But without reasonable dimensioning. I would follow the Powerint example, making the C with series R double the direct connect C, and adjust series R according to resonator impedance. In case of doubt, run a parametric analysis varying the R value. Resistor losses in normal operation and with allowed harmonic frequencies (see IEC 61000-4-13) must be considered when selecting the resistor rating.

 

[treez]

Hello,
Thanks FvM, that is good advice, though the lengths that one must take to mitigate the problem of switch-on overvoltage in switch mode LED lightbulbs are somewhat unknown it appears..ie use of X2 capacitors, in spite of their expense...

This LM3447 LED bulb design shows a 310VAC X2 film capacitor (C3) being used on the primary side DC bus. (schematic on page 5)
https://www.ti.com/lit/ug/sluua02/sluua02.pdf

This X2 capacitor (C3) is EPCOS B32921C3473M:
https://www.farnell.com/datasheets/51413.pdf

310VAC mains has a peak of 438V, though simulating the input filter of the LM3447 application design (with correct esr of inductors included) gives an overvoltage of 460V on C3. Obviously , 460V is more than 438V, and so somehow they have worked out that this X2 capacitor is able to withstand this switch-on transient overvoltage, which incidentally , lingers across C3 until the LM3447 gets going properly (after about 1 second).

So, is the use of X2 capacitors recommended for offline LED drivers in general?..or is it only recommended for Triac dimmable LED drives?

The input filter at switch-on is simulated in LTspice, (attached), and the simulation schematic is also attached.