Resonant frequency for a capacitor

[masoud23]

Hi
for example at Rifa's catalog for film capacitors the show Resonant frequency for each capacitor. I wounder how they calcolate it?

 

[colin55]

Provide us with more information about this . . . . and provide links or samples from the data you are talking about.

 

[Nigel Goodwin]

Just as you calculate any resonant circuit - although I expect it's measured rather than calculated - I don't see how you could measure it's self-inductance (which will be very small), apart from measuring it's resonant frequency and calculating the inductance.

 

[BrownOut]

Typically, the capacitor leads are connected together, forming a loop, and a frequency is connected across the cap. Then the frequency is swept to find the resonate frequency. The measurement takes lead inductance into account.

I have no idea how chip caps are measured.

 

[masoud23]

Hi
OK! But if I want to build and LC filter to suppress frequencies around 150KHertz, how do I calculate value for L and C. If there is not a short answer to this can someone refer to some good articles or books about this?

Tanks in advance

 

[Nigel Goodwin]

You simply need to design an LC filter, there are endless filter design programs available on line - none of it has anything what so ever to do with the self resonant frequency of a capacitor (which must be the most useless specification on a datasheet ever).

 

[crutschow]

You simply need to design an LC filter, there are endless filter design programs available on line - none of it has anything what so ever to do with the self resonant frequency of a capacitor (which must be the most useless specification on a datasheet ever).

That's actually in there for a good reason. It's sometimes necessary to know the self resonant frequency of a cap where it will not act as a pure capacitor, such as when designing high frequency filters or decoupling circuits. Obviously if the filter frequency is near the cap's self resonant frequency, the filter will act quite differently from the intended design.

 

[MikeMl]

The self-resonance of a capacitor is "series-resonance", where the inductance of the leads resonates with the capacitance. If the capacitor is used to bypass high-frequency RF, the series inductance is critical. For example, a 0.001uF disc ceramic works well as a bypass at 200MHz if the leads are ~1/4" long.

At 150kHz, you dont need to worry about a capacitor's series resonance...

 

[Nigel Goodwin]

That's actually in there for a good reason. It's sometimes necessary to know the self resonant frequency of a cap where it will not act as a pure capacitor, such as when designing high frequency filters or decoupling circuits. Obviously if the filter frequency is near the cap's self resonant frequency, the filter will act quite differently from the intended design.

As MikeMl has already pointed out, it's of no use what so ever for 150KHz, only of use at very high frequencies (and not much use then really, if you don't already knoiw what capacitors you should be using, you shouldn't be building VHF/UHF gear ).