Würth Elektronik 2022 17
Figure 7: EMC measurement with input filter and aluminum polymer capacitor C
IN
(Source: Würth Elektronik Group)
-20
0
20
40
60
80
100
100 kHz 1 MHz 10 MHz
dBµV
Frequency
Average QPeak CISPR 32 Average CISPR 32 QPeak
30 MHz
150 kHz
It can be seen that by changing only one component, the EMC
performance was significantly improved. The voltage drop generated
by the fundamental frequency and the first harmonic of this frequency
are reduced, generating less interference. However, the limit could
not be met, so further filters have to be placed. The structure of the
input filter was based on datasheet information. The filter's insertion
loss (in a 5Ω system) is shown in Figure 6. The input filter was then
included on the PCB, and another measurement was performed.
The result is shown in Figure 7, where the interaction between
the aluminum polymer capacitor and the input filter is visible. The
combination of input filter and low ESR and low ESL of the polymer
electrolytic capacitance make it possible to push the level broadband
below the limit of class B. Values of less than 40dBμV (average and
quasi peak) are easily possible (compared to the first measurement
with around 100dBμV), so the measurement is passed.
Figure 6: Built-in input filter with simulated filter performance (Source: Würth Elektronik Group)
-140 dB
-120 dB
-100 dB
-80 dB
-60 dB
-40 dB
-20 dB
0 dB
100 kHz 1 MHz 10 MHz 100 MHz 1 GHz
Frequency
Attenuation
