Patent ID: 6781444
Filing Date: 2004-08-24
Classification: H02M

Abstract:
An active EMI filter for reducing common mode noise current in a circuit comprising a rectifier coupled to an AC network, the rectifier supplying DC power to a DC bus, the DC bus feeding an inverter stage for providing AC power to a load, the load having a ground return line to a ground connection of the AC network, the active filter comprising:a plurality of transistor stages coupled in series, each of said transistor stages comprising two transistors; a main current sensor for sensing the common mode noise current in said circuit, said main current sensor comprising a current transformer having a primary coupled to a branch of said circuit in which common mode noise current occurs; the main current sensor having an output coupled to each of the transistor stages, the transistor stages being driven by said output in response to the common mode noise current; at least one capacitor coupling said transistor stages to said ground return line, said at least one capacitor providing a cancellation current to said ground return line from said transistor stages to substantially cancel the common mode noise current in the ground return line.