Choice of capacitor for low pass filter

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arunbhaskar

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I've designed a low pass active filter(Sallen-key second order) with cut-off frequency 5 Hz. I've used paper capacitor(value 1uF) which looks like this:



Is it ok for my application? I'm asking this because I heard that choosing the right type of capacitor is very important for the circuit to work correctly because different capacitors are optimized for different frequencies.
Thank you.
 

Look its datasheet in datasheet it should be defined which frequency range that your capacitor supply.I think that your frequency is low.For this reason you dont have to care the frequency range.In RF and Microwave the quality factor(Q) of the component decreases with the frequency so if you work high frequency systems you should care the frequency range.Instead of this you can look the other frequencies such as voltage etc.
 
Paper capacitors are very old and might fail soon.
I use accurate but inexpensive metalized plastic film capacitors for audio circuits.
 

Low frequency filters require relatively large time constants - resulting in large capacitors and/or large resistor values. In this context, it is important that the technologie of the capacitors does not lead to leakage effects (parasitic parallel resistances) which come close to the used resistor values and/or to the (neglected) opamp input resistors. Thus, low frequency filters have some problems which middle or high frequency filters do not have.
Recommendation: Use high quality capacitors.
 

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