LC filter problem calculating with DC voltage source/no resistive losse

[devilwiss]

Hello

I'm having a problem with unloaded series LC filter calculating, in fact if a source voltage has no component at resonance frequency of the LC filter the output voltage will be also free of resonance frequency component, but when simulating the circuit on PSIM, i found that this component exist !!

there were no resistors in the circuit even ESR ones (just 10VDC voltage source and the series LC 10mH with 10mF)

so how can i calculate its amplitude since the tranfer function is infinite and the input voltage at resonance is 0.

Thanks

 

[FvM]

I presume you are talking about a LC low-pass, it has an ideal DC transfer function of 1.0. So what do you want to calculate exactly?

 

[devilwiss]

I want to calculate the response amplitude of a low pass LC filter at resonance freq.

 

[FvM]

I want to calculate the response amplitude of a low pass LC filter at resonance freq.

O.K., why are you writing "DC voltage source" then? To analyse the transfer function, you have to connect an AC source. Or you analyze the behaviour in time domain, also not pure DC.

It's true that a pure LC filter with short or open source and load has infinite Q and infinite resonance amplitude. It's pointless to calculate it's transfer function.

The most interesting point involved with your question is that a real supply voltage LC filter must have limited Q respectively sufficient loss elements (either in the filter or the load) to achieve acceptable dynamical behaviour, e.g. overshoot with source or load transients.

 

[devilwiss]

This wasn't my question.

The problem is that i have a DC voltage source and i'm getting in the output of the filter a DC component(at the same amplitude of the source) plus a sine wave.
I want to calculate the amplitude of this sinewave !!


Thanks a lot.