LC filter- filtering a square wave to sine wave

Hi I am using a Lc filter trying to 6k Hz square wave to 60Hz sine wave, I used this equation 2*pi*f=1/(L*C)^(1/2) to calculate the value of the capacitor value because I pick the valus of the inductor is 1360 mirco H and rate 3A. the cutoff frequecncy is 60 Hz I used multisim and work pecfect, but when I build the auctual circuit that does not work.
Can anybody help me out and tell me how come that does not work.
Thank You

I'm sorry guy, Your question is unclear. Prehaps if You restste it and include what Your trying to accomplish?

kken6248 said:

Hi I am using a Lc filter trying to 6k Hz square wave to 60Hz sine wave, I used this equation 2*pi*f=1/(L*C)^(1/2) to calculate the value of the capacitor value because I pick the valus of the inductor is 1360 mirco H and rate 3A. the cutoff frequecncy is 60 Hz I used multisim and work pecfect, but when I build the auctual circuit that does not work.
Can anybody help me out and tell me how come that does not work.
Thank You

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Hi:

What kind of voltage/current are you intending to filter? Is it a square wave, or a pulse train?

Typically, LC passive filters are not very sharp, and you have to deal with fairly low Q as well in a real filter. Depending on the symmetry of your initial square wave, you may have to cutoff from the second harmonic onward. Also, if it is a pulse train, you will have to deal with core saturation of your coil as there will be a DC component.

All in all, if you need a passive filter (because the curcuit is high power, maybe?), you would be better off using a higher order LPF.

Jem

You can't obtain a 60Hz component from 6KHz square wave using a low pass filter, because a periodicaly wave(square in your case) have frequency components only from base frequency(6KHz in your case) up. If input wave is periodical then it have a periodical spectral structure, started from base freq.(f) where is the first sin component, the next sin component is at 2f, the next is at 3f and so on, but the next superior component have a low amplitude than the previous one and so on. All these components are sin, and represent the spectral structure of the signal.
If you want, for example, to filter only base freq to have a sine wave from a square one, you can use a low pass filter with a freq a little bit higher than freq of first component=base freq.

You can use a freq divider down to 60Hz and after that use a low pass filter to keep only first(fundamental) component if you use a digital divisor.