Electronics > Beginners

High frequency capacitor selection

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ZeroResistance:

--- Quote from: imo on August 14, 2018, 11:03:21 am ---@ZeroResistance: better you define the required capacity (in nF/uF) at specific frequencies, max currents (Ip-p), voltages(Vp-p), and other params you are aware of, and the experts here may identify the proper caps for you easier.

--- End quote ---

Problem being I looking for various values from 1000pf to 100pf, i might connect these in series or parallel to get the desired tuning.

Twoflower:
I was suggesting that you should get in contact with Murata to get a complete data sheet. Unfortunately I don't have the max peak current or other values than shown on the web. They seem to be very stable over a wide range of values. But your capacitance ranges might strike them from the list.




T3sl4co1l:
C0G ceramic or silvered mica.

If you're doing that much voltage into any significant amount of capacitance (let alone 1nF), you're probably looking at doorknob or pot type capacitors, possibly with water cooling.

Maybe just salvage a diathermy machine (that sounds like what you're doing, anyway!).

Tim

bson:
A 90V 15MHz resonator?  That sounds like volcano-dwelling mad scientist stuff to me... :)

ZeroResistance:

--- Quote from: dmills on August 14, 2018, 11:43:40 am ---The reason the applied voltage limit drops with frequency, is that you are really hitting a current limit!

Xc drops with increasing frequency, so the voltage you can apply without exceeding the maximum rated current (Yes, there always is one) drops with increasing frequency.

What you probably want are 'doorknob' capacitors used in high power transmitters, these are specified for RF current handling and voltage.

ATC make excellent parts but mainly for higher then the wiggly DC that is 13.56MHz.

Regards, Dan.

--- End quote ---

At 1Mhz the Xc of a 1nF capacitor is 160 ohms.
So If I take the actual rated voltage of 250V rms the current is 250/160 = 1.5A rms.
and If I take the max allowed volatge of 90V rms @ 1Mhz the current is 90/160 = 0.56A rms.

I still don't see why 1.5A * 1.414 = 2A peak should cause damage to a capacitor, especialy a pulse rated capacitor. What am I missing here?

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