Hello Group,
I am working with and electronic device which contains and audio output.
During a low frequency conducted immunity test, a tone can be heard at the
output of the audio section with a frequency equal to that of the test
frequency. The test starts at the lower end of the audio spectrum [~400Hz]
and progresses over time up to the top end of the audio spectrum [~30kHz].
I would like to be able to filter the conducted noise from getting into my
electronic device. This is an automotive application, so if I am
unsuccessful alternator noise may also be heard in my audio signal during
normal operation in the vehicle.
I have tried a few things to reduce the amount of noise such as:
1. LC filter with a cutoff at 1kHz
2. Series inductance [large amounts ~ 3mH]
3. Various common mode choke types, each with different core
materials [ie. iron core, ferrite core, etc....]
#1 helped some, but is not effective enough, #2 was very successful, but
the size of the choke would be enormous and not practical in this
application, #3 was not effective
Can anyone suggest an improvement upon the three methods above, or suggest
something different?
I would like to implement something on the board itself if possible, but
modification to the harness may be possible if necessary.
Thank you in advance for any help!
Regards,
Scott Mee
EMC Engineer
Johnson Controls Inc.
PH: 616.394.2565
EMAIL: scott....@jci.com
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