Differential & Common combination

Combination Differential Common Mode Choke and Inductor

Used as common mode choke but the circuit also has a DC bias or imbalanced AC power.

Differential-mode choke is used to filter electrical noise signal that appears on each of two lines (high and low line) of a closed loop, with current flowing in opposite directions. Sometimes a differential mode inductor is used one on each the high line and another one on the the low line. In such as case, 2 differential mode inductors are used in each circuit loop. The differential mode noise interference appears in series with the desired electrical signal. These electrical noise can be reduced by using an inductor in series with the high side and/or low side (ground) of the power line and by using a shunt capacitor across the 2 lines.

On the other hand, a common-mode EMI noise signal appears on the high and the low signal lines simultaneously in the same direction and phase. The common mode noise signal on each high line and low line returns through a common ground. A common-mode choke has 2 sets of windings on the same core with opposite polarity. When connected to the high line and low line on the same cores with opposite polarity, equal and opposite magnetic fields are generated on the core that cancels out the flux produced by the current flowing through the core, except the common mode noise that are filtered out by the inductor. A capacitor from each line to ground is also used.

In some application, there are both common mode noise and differential mode noise on the high and low lines such as a power line with DC bias or imbalanced AC currents on each lines. In such an application, the combination common mode differential mode choke is a good choice to use. However, because the cores cannot go into saturation due to the differential mode current (DC bias current), a lower permeability iron powder cores are used, and as such the common mode filtering is much lower than a ferrite based common mode choke with the same number of turns.

These 2-phase combination common mode/ differential chokes are wound on a distributed gap compacted powder cores with lower permeability than the regular high permeability Ferrite or Nanocrystalline and Amorphous ribbon based cores. By winding 2 windings on distributed gap iron powder cores, each winding acts as a differential mode chokes as well.