Regarding the quality of the current waveform, it is possible
to consider three types (see Fig. 3). On top, the sinusoidal
waveform usually involves a high-cost circuit. An intermediate
quality level is composed by those solutions that comply with
the regulations without achieving unity power factor. Among
them, there are the so called “single stage converters” that offer
some advantages, but its field of application is limited to low
power (up to 300 W, approximately). Finally, if there is not
any requirement about the line current, the simplest solution
composed by a diode bridge and a filter capacitor can be used
as a first stage.