I am going to build a low voltage and low power Modular Multilevel Converter (MMC) for research purposes. In each phase of MMC, there are two inductors where low frequency (50 Hz) currents pass through. On the other hand, I need inductors with few miliHenry inductace that can tolerate low frequency currents of a few amps (e.g. 5A).
I am having hard time finding such inductors on digikey or RS or Farnell. The only one that I've found is this common-mode choke, but I am not sure if it can be used as an inductor for the mentioned application or not.
Any ideas?
Electronic – Using Common-mode choke as inductor
chokeinductorpower electronics
Related Solutions
The USB signal is not entirely differential, so it's not a great idea. (The end-of-packet (EOP) signal is both pins pulled low, which, I believe, is why there's always noise at 1 kHz and harmonics in USB systems, since it's sending common-mode signals every 1 ms.)
- A common mode (CM) choke should be used to terminate the high speed USB bus if they are need to pass EMI testing. Place the CM choke as close as possible to the connector pins. See Section 5.1 for details.
Note: Common mode chokes degrade signal quality, thus they should only be used if EMI is a known problem.
Common mode chokes distort full speed and high-speed signal quality. The eye diagram above shows full speed signal quality distortion of the end of packet, but still within the specification. As the common mode impedance increases, this distortion will increase, so you should test the effects of the common mode choke on full speed and high-speed signal quality.
High Speed USB Platform Design Guidelines
Note: additional filtering may be achieved by winding the 4 wires through the ferrite bead an additional turn. As with the use of ferrite beads in signal paths, care should be taken to insure that the signaling meets rise and fall times, especially the EOP signaling. EOP signaling is single ended and may be strongly affected by a single bead, which acts as a common mode only filter.
Your assumptions are spot on.
Another thing to bear in mind is that any leakage inductance between the common-mode windings manifests itself as a parasitic differential mode inductor - this is why it's common to see toroidal common-mode chokes with the windings opposite each other (not interleaved) to maximize leakage inductance and get that 'free' differential mode filtering.
Best Answer
This is just a stab in the dark pointer that hopefully indicates the size of inductor core needed....
A good permeability ferrite core might have an inductance of 10 uH for one turn and, to get 1 mH you need 31 turns because inductance is proportional to turns squared.
So, with 5A RMS the peak current is about 7.1 amps and that's an MMF (magneto motive force) of 219 amp-turns. Given that the mean length around a fairly sizable ferrite is about 40 mm, the H field (amp-turns per metre) is going to be 5480.
If the relative permeability of the core is about 3000 and remembering that µ0 = 4π × 10^−7, the resultant flux density will be 5480 x 3000 x µ0 = 21 tesla and too much for a ferrite (and also iron) core of the mean length mentioned above. Ferrite starts to saturate generally at about 300 mT.
So, get looking for something that is quite large - nothing ferrite will work as far as I know - it will probably need to be laminated iron and the size of a small transformer. Something you could comfortably hold in the palm of your hand and would weigh about half a kg (maybe a tad less).