Capacitance and inductance of passive filter

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Discussion Overview

The discussion revolves around calculating the values of capacitors and inductors for a passive filter design, focusing on the parameters of voltage, frequency, and the absence of current. Participants explore the implications of these parameters on the selection of components for effective filtering.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant expresses difficulty in determining the values for a capacitor and inductor given a voltage of less than 1 volt and a frequency of 60Hz, without knowledge of the current.
  • Another participant suggests that current is not necessary for the calculations, emphasizing the importance of frequency, capacitance, and inductance.
  • A participant requests equations to determine inductance and capacitance, questioning how to establish these values with only frequency available.
  • It is proposed that both inductance and capacitance are free parameters, but practical applications require realistic component values, which may be limited for low frequencies like 60Hz.
  • Concerns are raised about the feasibility of achieving desired filter characteristics at low frequencies without using active filters or expensive components.
  • Questions are posed regarding the specific type of filter being designed (e.g., low pass, impedance) and the relevance of filter types such as Chebyshev, Butterworth, and Elliptical in determining component values.
  • Another participant mentions that voltage and current considerations are relevant when assessing power handling requirements.

Areas of Agreement / Disagreement

Participants do not reach a consensus on how to proceed with the calculations, and multiple viewpoints regarding the necessity of current and the types of filters remain. The discussion reflects uncertainty about the best approach to selecting component values for the passive filter.

Contextual Notes

Limitations include the lack of specific equations for determining component values and the challenge of finding suitable components for low-frequency applications. The discussion also highlights the dependence on practical considerations in filter design.

Idea04
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I'm having some trouble calculating the values I need for a capacitor and inductor for a passive filter. The values that I know to use are current, voltage and frequency. But I have a voltage <1 volt and a frequency of 60Hz but no current. Can someone help me figure out what value of capacitor and inductor to use.
 
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Idea04 said:
I'm having some trouble calculating the values I need for a capacitor and inductor for a passive filter. The values that I know to use are current, voltage and frequency. But I have a voltage <1 volt and a frequency of 60Hz but no current. Can someone help me figure out what value of capacitor and inductor to use.
You don't need to know the current. Just the frequency, capacitance and indunctance.
http://mysite.du.edu/~etuttle/electron/elect31.htm"
 
Last edited by a moderator:
Do you have an equation to figure out inductance and capacitance. If I don't have the capacitor or inductor how do I determine what the inductance and capacitance is. All I have is the frequency.
 
There is no equation; both are free parameters.
However, in real applications you need real componenents. If you take a look at what is available you will quickly realize that the range is actually quite limited; you can't buy a 100F capacitor or a 1 fH inductor. You need to find a combination of values that give you the right frequency and at the same time result in realistic values for C and L.

Which, by the way, can't really be done at 60Hz; for frequencies that low you need an active filter (unless you are willing to spend a LOT of money on the type of huge chokes used in e.g. tube amplifiers).
 
What sort of filter? For what? Low pass? Impedance? Roll off? Ultimate attenuation?

There are plenty of filter types .. Chebyshev, Butterworth, Elliptical, Constant K. These will have low passband ripple if terminated with the current i/p and o/p impedance.

There are probably on-line calculators to give you the component values.

Voltage and current only come into when considering the required power handling.
 

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