Technical Reference Notes

AEO_ALO04/12/20/25x48 Series

MODEL: AEO_ALO04/12/20/25x48 SERIES

SHEET 23 OF 26

AUGUST 25, 2005 - REVISION G

Input Filter for FCC Class B Conducted Noise

A reference design for an input filter that can provide FCC Class B conducted noise levels is shown below (See Figure 61).

Two common mode connected inductors are used in the circuit along with balanced bypass capacitors to shunt common mode

currents into the ground plane. Shunting noise current back to the converter reduces the amount of energy reaching the input

LISN for measurement.

The application circuit shown has an earth ground (frame ground) connected to the converter output (-) terminal. Such a

configuration is common practice to accommodate safety agency requirements. Grounding an output terminal results in much

higher conducted emissions as measured at the input LISN because a hard path for common mode current back to the LISN is

created by the frame ground. “Floating” loads generally result in much lower measured emissions. The electrical equivalent of

a floating load, for EMI measurement purposes, can be created by grounding the converter output (load) through a suitably

sized inductor(s) while maintaining the necessary safety bonding.

Figure 61: Class B Filter Circuit

PARTS LIST

CKT CODE

DESCRIPTION

Common

Mode Choke

CTX01-15091

Cooper Electronic

Technologies

X-Cap

0.47 µF X 4pcs

Y-Cap

22 nF X 4 pcs

Cin

220µF X 1pc

FILTER