MKP Self Healing Problem

[onders]

Hello,
I am interested with the Self healing property of Metallized Polypropylene X2 capacitors.

Actuallay we'd a recent problem in some of our electronic boards which are using capacitive supplies and X2 capacitors as a current limiter. However, we'd faced with Zener diode problems in those boards which we use 2.2uF and 1.5uF X2 capacitors. Regarding to the current limiting mission of X2 capacitors, our main suspect in this failure is X2's because of its Self healing property. While Self healing is happening, X2 is short circuited for a small period and only the 33 ohm resistor is active during SH so large amount of energy passes through the X2 and burn one of the /both of the Zener diodes.

I have attached our supply scheme as an appendix.

I do appreciated for your precious comments.

Best regards,

[linuxguru]

Re: MKP Self Healing Problem

I suppose you do realize that this a a hot chassis design, which is utterly unsafe for most household and office use. It might even be illegal in most of the EU.

What is the voltage rating of C6? It needs to be at least twice the peak main voltage, i.e. 2*1.4*220. You need to use 630v at the minimum. Also, I can't understand the purpose of C4, unless it is some kind of EMI/RFI compliance component, which seems to be a contradiction, given that this circuit is probably prohibited in most parts of the world that monitor compliance.

[gonzo0815]

Re: MKP Self Healing Problem

Hm... if you put it in an isolated case with no metal or other conducting material it should be fine i think. In circuits like trailing edge cut off dimmers, similar desings for uControer supply are used.