I'm reviewing a set of inductors for the Experimenting with Magnetic Components design challenge. In this post: make a custom inductor
|
Balanced Twisted Windings Common Mode Choke
I'm designing a sister for the common mode choke that was used in the previous post.
There are several ways to wind a common mode choke on a coax core.
The easiest is to wind each inductor on one side of the core, Both in the same direction.
To reduce the magnetic field that's emitted from the device, you can use another technique: twisted wire winding.
This will concentrate the magnetic field in the inside (eye) of the core.
I used 12 13 windings for each inductor. 6 turning right, then cross over and under, then 6 left windings.
Parts
You need a ferrite core. I used a small diameter one from Lairdsmall diameter one from Laird (datasheet).
Get some enameled copper wire from the transformer of a defunct device. Take wire that can be handled with ease.
Optionally, masking tapemasking tape.
The components were part of a shopping cart I won with Project14.
Core specifications:
Laird 28B0375-400 ferrite cylindrical core, 81 ohm, 4.83 mm length, 5.08 mm inner diameter, 9.53 mm outer diameter
NiZn ferrite
image source: Laird datasheet
Measurements
It would be great if someone that owns a magnetic field probe could measure the difference in emission of both winding options.
The twisted wire one should have a much smaller magnetic field, concentrated inside the core. The common one's field spreads on the outside of the core.
With an LCR meter, the two inductors measure almost identical.
12 13 turns (6 left, 6 right and the crossover one in the middle) for both.
Frequency: 100 kHz
| attribute | inductor a | inductor b |
|---|---|---|
| L | 66.85 µH | 67.01 µH |
| Q | 5.99 | 5.97 |
| ESR | 7.05 Ω | 7.05 Ω |
| ϕ | 80.4° | 80.4° |
| D | 0.168 | 0.167 |
| RS | 7.042 Ω | 7.045 Ω |
| DCR | 0.09 Ω | 0.09 Ω |
In the next post (or in the comments), I'll try to show the common mode rejection capabilities.
