Four leg chokefor common-mode rejection

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The three-phase choke with common-mode rejection serves as a standard filter choke. The fourth leg is used in this case for common-mode rejection.


  • Compact contruction compared to single-phase inductors
  • One part instead of 3x single phase and therefore a significant price advantage
  • Lower power losses as a single choke

The magnetic coupling of three phase filter chokes poses the challange at complex filter systems. Therefore, depending on the topology of power electronics, single-phase chokes will be applied.

If the currents are asymmetric, the inductances of the conventional three-phase chokes do not act in the same way as the one-phase winding goods; therefore the magnetic flows cannot be compensated and this causes a heating in the iron. If all currents of all three phases flow in the same direction at the same time, the three-phase choke only operates with its leakage inductance.

An alternative to the one-phase chokes are four-and five-leg chokes; developed by Schmidbauer! Another advantage: asymmetric load of the phases is possible.