What used to 200W filter capacitors on 13.5 MHz?

[carpenter]

I have a transistor that switches 200W (3-4A) at 13.5 MHz for induction heater.
Behind the power transistor is LC filter 9th, which cuts off interference. Coils are iron powder toroids T130, Capacitors in size to hundreds of pF.
The question is What type of capacitor used?
The professional design were used mica capacitors, availability and price of mica capacitor, especially in SMD is quite tragic.
Do you think it would be possible to use ceramic capacitors NP0, 1206 size ?

 

[chuckey]

Have you calculated the rf current through the caps? and the voltage across them? From this and their loss angles you can work out how much power they will dissipate. There is a good reason why professionals use mica caps do you think you can do better?
Frank

 

[carpenter]

Voltage across thing twice the working DC voltage. Current can not calculate from the known data.
I also used mica capacitors, but their availability and price in a small and SMD is just tragic
Therefore, seeking compensation, and no logical first choice is ceramics

 

[sabouras]

Use high voltage RF ceramics from atc or kemet or avx. They have series that cover your needs.

 

[RF_Jim]

Voltage across thing twice the working DC voltage. Current can not calculate from the known data.
I also used mica capacitors, but their availability and price in a small and SMD is just tragic
Therefore, seeking compensation, and no logical first choice is ceramics

You say: "Current can not calculate from the known data."

This is what differentiates engineers from simple 'users of technology' - which is everybody else.

Recommend running a SPICE simulation of the filter using *measured* (harmonic and fundamental signal levels) from your 200 W RF 13.56 MHz source and then use those values as the *exciting* signal source in SPICE simulation.

Doing this one can 'observe' each branch circuit (as set up in the SPICE input file V or I measure statement) and series circuit component's current value and voltage looking for cases where the component specification might be violated.

Even if alternative components are chosen, to assure design within limits of those parts requires an engineer to ascertain via quantitative data the operating currents and voltages for each components rather than just canvassing 'consensus' from among one's peers.


RF_Jim


PS. Be extremely careful measuring the output RF signal from the 200 W 13.56 MHz source! Be sure to use appropriately rated RF 50 Ohm loads and couplers and so forth so as not to damage any test equipment (like the spectrum analyzer!) or yourself!