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  1. #1
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    Choice of capacitors for DC blocking and 3A AC?

    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.

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    Re: Choice of capacitors for DC blocking and 3A AC?

    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
    Please don´t contact me via PM, because there is no time to respond to them. No friend requests. Thank you.



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  3. #3
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    Re: Choice of capacitors for DC blocking and 3A AC?

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



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    Re: Choice of capacitors for DC blocking and 3A AC?

    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

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  5. #5
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    Re: Choice of capacitors for DC blocking and 3A AC?

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



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  6. #6
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    Re: Choice of capacitors for DC blocking and 3A AC?

    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.



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