PFC Controller or Power Factor Correction Controller is a front end circuit that is used in AC-DC power supply for improving the power factor and power quality. It is usually used in between the rectifier and the smoothing capacitor of power supply circuits. The PFC controller reduces the harmonic distortion in the supply current and thereby creates an input AC line current waveform in-phase with the sine input voltage waveform.

Non-linear loads such as SMPS generates harmonic currents. As a result, the shape of the input AC line current wave changes into a non-sinusoidal and therefore, reduces the power factor. This harmonic distortion in line current degrades power quality. Hence, the PFC controller is used to avoid input current harmonics by minimizing the interference with other devices being powered from the same source. It also improves the power factor significantly to ensure electrical efficiency of the power distribution system.

The PFC controller can be classified into two - passive PFC circuit or active PFC circuit. The passive PFC circuit uses passive elements such as inductors or capacitors to filter the harmonic currents and thereby improving the power factor. An active PFC circuit is a type of booster circuit that is used to filter the harmonic currents & improve the power factor. It consists of a diode, a power transistor (typically MOSFET), an inductor, and a PFC control unit that controls the ON and OFF time of the power transistor. 

PFC controllers are ideal for use in AC to DC supply circuits of electronic lamp ballasts, SMPS, home appliances, motor drives, audio visual equipment, laptops, consumer electronics, and other main connected electronic devices with a higher rating (typically, more than 75 W). 

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