Is it possible to combine different resonant capacitor ratings in the resonant tank of the LLC converter?

Thread Starter

DeltaVetal

Joined Dec 4, 2020
3
Hi all,


I'm calculating the components for a powerful LLC converter (3.3kW max).

At the moment I choosing capacitors for the resonant tank.
In general, I need to dial 62nF.

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If using film capacitors, then I found 10nF and 1nF. I can connect x6 10nF capacitors and x2 1nF capacitors in parallel. Will come out about 62nF (accurate).

If I understand correctly, then the current entering the resonant tank will be evenly distributed between all parallel capacitors.

The only thing I did not find an answer is whether it is good that in this combination two capacitors have a capacitance of 1nF, and the rest - 10nF. Will this somehow overload small capacitors?
 

ronsimpson

Joined Oct 7, 2019
1,125
The current will divide by the value of the cap.
If you have six 1uF caps each will see 1/6 of the current. But if you have (5*1uF and 2*0.5uF) then each of the 1uF will see 1/6 and each of the 0.5uF will see 1/12 of the current.
 

Ian0

Joined Aug 7, 2020
1,158
Choose the capacitors carefully - don't forget there is a current of 10Amps going through them. Most film capacitors are designed for signal use and not for that amount of current. Read the datasheets!
And don't forget the voltage rating. The resonant tank voltage can easily exceed the supply voltage. At 3.3kW on a 325V supply and 100kHz there will be 330V rms across 62nF, twice that at 50kHz.
 
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