Choice of capacitors for DC blocking and 3A AC?

[carpenter]

You will deal with choice and sizing DC blocking capacitors for RF power amplifier.

- DC voltage on RF transistor is under 48V
- Frequency is over 10MHz
- AC Current max 3A sinus

Is a good choice use 1206 ceramic X7R 100nF 200V, 6 pcs in parallel (500mA over each) or it's a problém?

Xc for 1pcs od 100nF < 150mOhm for 500mA is power disipation on C under 40mW on 6pcs <240mW.
Question is how big will be ESR on this type of capasitors?

I was thinking about 2x 330nF PP WIMA , but they are big.

 

[KlausST]

Hi,

I see no problem.

Don't use Xc for power dissipation calculation, only ESR....which should be much less than Xc.

Fir detailed informations I recommend to consult the datasheet.

Klaus

 

[Easy peasy]

NP0 is a better choice at >10MHz ...

 

[FvM]

With effectively no voltage across the capacitor, X7R should be o.k. Major manufacturers have individual datasheets for capacitors, see e.g. Murata 100nF/250V/1206

 

[Easy peasy]

its nearly resonant at 18MHz, so OK at 10MHZ, just, but not any higher, possibly better to have several 33nF ... in parallel

 

[FvM]

Choosing the capacitor for exact series resonance is of course possible, but we have to consider the complete circuit. At the end of the day, the capacitor ESL is probably a small fraction of the total circuit series inductance. Using the example capacitor up to 100 or 200 MHz @ 500mA shouldn't be a problem.