A new input current shaping technique using converters operating in continuous conduction mode

A new input current shaping technique has been proposed. Its operating principle is based on the connection of an additional DC output, obtained from the converter´s transformer, between the input rectifier and the bulk capacitor in a conventional switching-mode power supply with no power factor correction. This additional output is a forward-type one with one extra inductor, which provides an effective duty cycle modulated by the input current. Thus, the voltage-current characteristic of this output consists of a voltage source and a loss-free resistor, connected in such a way that they help the diodes of the line rectifier to conduct. The main difference with other input current waveshapers lies in the fact that the filter inductor of the additional output operates in continuous conduction mode. Thus, the current stress in the power transistor is minimized. With the final topology, a good trade-off between bulk capacitor voltage, re-cycling energy, power factor and harmonic content can be established in order to comply with the IEC 1000-3-2. Many aspects in the design and operation of this type of converter are analyzed in this paper