Problem selecting high voltage resonant capacitors for LCC Converter

Thread Starter

SiCEngineer

Joined May 22, 2019
320
Hi,

I have designed an LCC split-capacitor converter and while browsing the data sheet for my resonant capacitors, noticed how much the AC voltage of an MLCC C0G type derates with frequency. My converter is running 200-400kHz. Here is the data sheet: KEM_C1039_KC_LINK_C0G-1315560.pdf (mouser.co.uk).

I originally have been using the CKC21 version of the capacitors, which are not good enough for voltage or current. I was using 6 of these, 3 in parallel for each of the upper and lower parallel connected branches of the split-capacitor bank. An option is to upgrade these to the CKC33 capacitors which have better voltage and current capabilities with frequency, but they are £8 per capacitor at Mouser and are almost double the size of the CKC21 versions. If I can fit these on the board, it will be fine and problem over.

However, I am considering instead having some smaller capacitors connected in series/parallel. So, rather than having 4.7nF x 3 x 2 (~29nF) I would have 10nF x 2 (Series) x 3 x 2. These can come in smaller case packages and would half the voltage across the capacitors, but there would be twice as many and more losses due to additional ESR. I am also worried about reliability of connecting them in series this way. Here as an example of a component: C3225C0G3A103J250AC TDK | Mouser United Kingdom. Furthermore, TDK does not give any advice on maximum current through the capacitor, which would be less than the 2220 package I originally had selected.

Can anyone offer any advice? Which solution seems to be the better option?

Regards,
SiC
 

Thread Starter

SiCEngineer

Joined May 22, 2019
320
I have found the following which shows current rise with temperature, I supose this is the limiting factor for maximum current: Characterization Sheet (tdk.com)

But I do not see any suggestions regarding maximum AC voltage for the capacitors with frequency. If they are rated at 1kVDC, and I operate them in series such that there is about 250VAC across them, should this be suffice?
 
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