# Low-pass LC butterworth filter cutoff frequency question

1. Jun 3, 2013

### mehrlin

I am designing a 5-pole low-pass butterworth filter to have a cutoff frequency of ~50 Hz. It has a source impedance of ~1 Ohm, and a load impedance of ~50 Ohm (The load impedance can be changed around if that will help later). Because of these, I am using the "T" configuration. I used the table in the back of The Art of Electronics by Horowitz and Hill, to determine the following values:

L1=245.9 mH
C2= 107.9 uF
L3 = 220 mH
C4 = 56.9 uF
L5 = 49.18 mH

The problem, however, is that I am unable/unwilling to order custom parts with these exact values. Thus, I have chosen parts with the following values:

L1=250 mH
C2 = 100 uF
L3 = 220 mH
C4 = 56 uF
L5 = 50 mH

My question is now what will be the actual cutoff frequency for these values? I have thus far been unable to track down an equation that will help me find this.

2. Jun 3, 2013

### carlgrace

Download LTSPICE from Linear Technolgy (linear.com) and simulate it. You should always simulate something before you build it, anyway.