Technical Reference Notes
ALD12/18/20/25 Series
(Single Output 16th 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 42). 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.
PARTS LIST
CKT CODE DESCRIPTION
CTX01-15091
FILTER
Common
Cooper Electronic
Mode Choke
Technologies
X-Cap
Y-Cap
Cin
0.47 µF X 4pcs
22 nF X 4 pcs
33 uF
Figure 42: Class B Filter Circuit
MODEL: ALD12/18/20/25 SERIES
AUGUST 17, 2005 – REVISION C
SHEET 17 OF 20
ASTEC [ Astec America, Inc ]
