# RL High-Pass/ Low-Pass Filters

Discussion in 'Homework Help' started by Petrucciowns, Jun 25, 2009.

1. ### Petrucciowns Thread Starter Active Member

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Does anyone know the formula to find the cutoff frequency for an RL High-Pass/ Low-Pass Filter?

I know with RC filters it's 1/ (2ΩRC) ,but this does not work for RL filters.

2. ### Petrucciowns Thread Starter Active Member

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I figured it out, but if anyone is ever looking for it it's:

Fc (Cutoff frequency) = R/ ( 2ΩL)

3. ### PRS Well-Known Member

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I believe its f = 1/(2*pi*R*L)

4. ### Petrucciowns Thread Starter Active Member

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Thanks for the reply. I already tried that one. It calculates the cutoff frequency of and RC filter. The one I listed above calculates the cutoff frequency of an RL filter.

5. ### Jony130 Senior Member

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Feb 17, 2009
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Well, of course the cut-off frequency is when XL=R
XL=ωL=2∏F*L
And the time constant for LR circut is L/R
Therefore, the cut-off frequency, no matter if High-Pass/ Low-Pass
fc = R/(2•Π•L)