It's a power entry part of a DAQ card, the bottom right is a DC jack. The power flow maybe:

Power DC jack -> ferrite bead -> cap -> common mode inductor -> cap -> ?

I guess the bigger black one may be a common mode inductor too. But I've never saw such a bigger one in this kind of package, and it seems it's full shielded, can't see the coils from side.

May anyone give some clues?

enter image description here

  • \$\begingroup\$ I would suggest you use GIMP or Photoshop or another program to assign ad hoc part ID's to each part you have a question about. A DVM and a LCR meter would go a long way toward solving what these parts are. Sure, some are obvious, but to estimate current flow from here to there without ref numbers is well, just guessing. We are not fond of guessing as we don't want to mislead the OP asking the questions. \$\endgroup\$ – user105652 Oct 20 '18 at 2:48
  • \$\begingroup\$ It would also help if you could zoom out just a bit so we can see more parts. \$\endgroup\$ – user105652 Oct 20 '18 at 2:49
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    \$\begingroup\$ My money is on a bridge rectifier, poke around with a meter in diode mode and see what you get. \$\endgroup\$ – Matt Young Oct 20 '18 at 2:49
  • \$\begingroup\$ @Sparky256 I've no electron microscope by hand, this is best what I can take using my cell phone. \$\endgroup\$ – diverger Oct 20 '18 at 4:15
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    \$\begingroup\$ I agree it looks like a common mode choke also. You could try measuring the DCR, I guess. \$\endgroup\$ – mkeith Oct 20 '18 at 5:47

Both the black doodads appear to be common-mode chokes. Really looks like ferrite rather than a molded semiconductor package. Test with a small magnet to confirm. Ferrite should be strongly attracted, otherwise it would just be the leadframe which isn't much metal.

So a bunch of filtering to keep hash from the switchmode power supply from getting out the power port (that black thing on the lower right is a barrel jack typically used for power).

There might be an option for a larger CM choke rather than the tiny one, judging by those unused pads.

Edit: Here's what I see. Mostly 100% sure, C5 is a bit iffy. The leftmost chip is probably a SMPS chip- looks like a diode below it, and probably an inductor out of shot above it. L1 and L2 are ferrite beads.


  • \$\begingroup\$ CM chokes are critical to good EMI egress results by raising the CM impedance but keeping DM impedance low which is filtered by the discrete LCL chips after jack. Low egress reduces the mutual coupling to long sensor cables with higher impedance. Critical for high CMRR that cannot be reduces with an INA of 120dB CMRR if the cable have 1% coupling or. CMRR of 40dB \$\endgroup\$ – Tony Stewart EE75 Oct 20 '18 at 19:46
  • \$\begingroup\$ Now, I suspect it's maybe a bigger CMC covered by a self made metal cover. Because apparently there is plenty space for some marking on it, but it has nothing on the shell. \$\endgroup\$ – diverger Oct 20 '18 at 23:23

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