Boost-buck push-pull converter for very wide input range single stage power conversion

In many avionics systems, the power supply is required to operate over a very wide input voltage range. In these aircraft systems the power supplies are powered off a permanent magnet generator (PMG). The PMG, which is typically mounted via a gear box to the engine of the aircraft, outputs a voltage proportional to the speed of the engine. It is usually required to have the avionics start at very low engine speeds and operate up to the maximum engine speeds. To operate over this large input range, power converter stages are cascaded to reduce the input range down to manageable levels. The last converter stage then provides the filtering, isolation, scaling and regulation for the avionics system. Additionally, aircraft power sources are provided for backup power and typically require power factor correction. Active power factor correction is also performed with a separate cascaded pre-regulator converter. Multiple power conversion stages reduce efficiency, increase cost, and increase size of the power supply system. The power converter described combines the aforementioned functions into a single conversion stage. The converter is a push-pull converter that has both buck and boost regulator characteristics. At low input voltage the push-pull converter acts as a boost, and at high input voltages it acts as a buck converter. For power factor correction applications, this push-pull converter, by transitioning between the boost and buck operating modes, is able to shape the input current.<<ETX>>