The EMI filter (Electro Magnetic Interference) is low pass filter for the DC power supply, the aim is to reduce significantly the transient interference coupled from the power line. It consists of a ground capacitor, an inductance series and another capacitor it can be as a screw pass-through capacitor, or for soldering, or for printed circuit board version or even SMD. The configuration can be greek P, T, or L depending on the circuit solutions.