ALO25F24 Datasheet, PDF (10/13 Pages) Astec America, Inc – Single Output 8th Brick: Open-Frame Module

Technical Reference Notes
ALO25F24
(Single Output 8^th Brick)
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 13).
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.
FILTER
PARTS LIST
CKT CODE
Common
Mode Choke
X-Cap
Y-Cap
Cin
DESCRIPTION
CTX01-15091
Cooper Electronic
Technologies
0.47 µF X 4pcs
22 nF X 4 pcs
220µF X 1pc
Figure 13: Class B Filter Circuit
MODEL: ALO25F24
AUGUST 23, 2005 - REVISION H
SHEET 10 OF 13