DAMPED EMI INPUT FILTER FOR POWER FACTOR CORRECTION CIRCUITS

摘要

An active damping circuit for an electromagnetic interference filter for a power factor correction circuit is provided which simulates a line damping impedance which actively varies according to the sensed line (22) current. The active damping circuit comprises an n-th order, Cauer-Chebyshev, low-pass filter having input series damping impedance (Zd) simulated with a power operational amplifier (20) and two high-frequency isolation transformers (T1 and T2). The simulated damping impedance offers greatly reduced size and power dissipation as compared to prior art passive schemes which typically require large impedance components for damping. A passive damping circuit is also shown which involves providing an alternate inductive current path in parallel with a damping resistor whereby lower frequency currents are diverted through the alternate current path and high flow through the damping resistor. In this manner, the damping action of the damping resistor is attenuated for lower frequencies but remains unaffected for higher fequencies.