Common mode (choke) coil

A filter element used to eliminate noise generated by the potential difference between the power circuit and the ground. It has a structure similar to a transformer, with two coils wound with equal turn ratios on a core, and the power side and load side wirings are connected to its four terminals. Unlike a transformer, it connects each of the two power lines in series with a coil. Since the currents flowing through the two power lines are in opposite directions and their magnetic flux cancels out without affecting each other, only the noise generated between the power lines and the ground can be eliminated. To enhance the noise removal effect, a core with high magnetic permeability is often used.