Common mode (choke) coil

A filter component used to remove noise generated by the potential difference between a power supply circuit and ground. It has a structure similar to a transformer, with two coils of equal turns ratio wound on a core, and the power-side and load-side wiring are connected to its four terminals respectively. Unlike a transformer, the connection method differs significantly, with a coil connected in series to each of the two power lines. Since the currents flowing through the two power lines are in opposite directions, the magnetic flux cancels out and has no effect, allowing only the noise generated between the lines and ground to be removed. To enhance the noise suppression effect, a core with high magnetic permeability is often used.