Patent ID: 6707690
Filing Date: 2004-03-16
Classification: H02M

Abstract:
A pulse width modulated apparatus to convert an input voltage to an output voltage at duty-cycles exceeding 50% comprising:a transformer having a primary winding coupled to a secondary winding, the primary winding including a plurality of segments, each segment from the others and having a high end terminal and a low end terminal, each terminal accessible within the apparatus; a first switch connected between a positive rail and a high end terminal of a first primary segment; a second switch connected between a negative rail and a low end terminal of a last primary segment; a number of intermediate switches connected between a low end terminal of a segment and a high end terminal of an adjacent segment, wherein each intermediate switch is interposed between a pair of segments to allow the full primary winding to function when all switches are closed; a plurality of pairs of diodes, each pair of diodes associated with a segment of the plurality of segments, a first diode of each pair of diodes connecting a high end terminal of the associated segment to the negative rail, a second diode connecting a low end terminal of the associated segment to the positive rail, wherein the diodes conduct for a part of the duty-cycle when the switches are open; and an output stage connected across the secondary of the transformer.