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RC damping for second order filter

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Selvam_Perumal

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Hi all,

When will we require damping circuit for a second order LC filter?
 

This is the type of filter which should have a load attached (say audio amplifier experts). The LC network has a resonant frequency. If that frequency comes through a low impedance loop, the LC network boosts its amplitude. If sufficient power is available then the effect runs out of control, and components can be destroyed. In other words, the filter needs to be damped.

I've been entertained by watching this effect in simulations. Theoretically it could be a means to boost sagging mains AC. However it is dangerous if no load is present. So it isn't practical for the consumer market.
 

Filters designed according to a filter prototype (e.g. Butterworth, x-dB ripple Chebyshev) have a well defined Q set by the ratio of LC impedance to real source and load impedance. The problem with power electronics filters is that they have often low real impedance termination and varying load and source impedances. In this case, artificial damping can be useful.

I often implement the damping as C-RC combination instead of a single shunt C in second or third order low-pass.
 

LC input filter can be used to reduce EMI. Instability of the supply occurs when the input impedance of the converter is smaller than the output impedance of the filter. So, you need to damp the filter so that its resonant peak stays below the input impedance of the converter.

I often implement the damping as C-RC combination instead of a single shunt C in second or third order low-pass.
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Output filter as well ?
 

Your question is too open ended - if for an inverter output - then yes always, other apps may not require any damping ...
 

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