I am using a ACM70V-701-2PL-TL00 Datasheet to attempt to filter out A/C ripple in an in-vehicle audio device. I've run the input 12v through one channel of the choke and I attached the other channel to the same ground pour on both ends.

This is not correct, is it? I assume that I should instead split the ground into two polygons with the choke bridging them, correct?

Right now, the choke is not effective, so I am trying to run through what I've done incorrectly.


  • \$\begingroup\$ Show your circuit please. \$\endgroup\$
    – Andy aka
    Mar 1, 2022 at 22:21
  • \$\begingroup\$ That won't filter ripple in the DC input, only common mode noise. \$\endgroup\$ Mar 1, 2022 at 23:13
  • \$\begingroup\$ @KevinWhite - RIght, I'm trying to filter AC ripple, not DC. :) \$\endgroup\$
    – t3ddftw
    Mar 2, 2022 at 1:47

1 Answer 1


Your L1 has become a transformer, with a short circuit on the secondary (pins 2 and 3). And as you stated, the secondary is grounded.

Therefore the primary impedance (pins 1 and 4) is a very low impedance, and not functioning as an effective filter.

I don't know if you are using the vehicle chassis as ground to carry return current to the battery.

If you simply want to use the choke as a single inductor (not common mode), then disconnect pins 2 and 3. This can effectively reduce ripple.

For the inductor L1 to act as a common mode choke, the return current to the battery must flow through the choke pins 2 and 3. This can filter common mode noise.

  • \$\begingroup\$ Thanks, I was hoping that was the answer -- I'll rewire the ground in two different networks that are unified through pins 2 & 3! Ground goes to a junction that is directly tied to the chassis, yes. \$\endgroup\$
    – t3ddftw
    Mar 2, 2022 at 1:53

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