The impending trends in the global demand of more-electric-aircrafts with higher efficiency, high power density, and high degree of compactness has opened up numerous opportunities in front of avionic industry to develop innovative power electronic interfaces. Traditionally, passive diode-bridge based transformer rectifier units (TRU) have been used to generate a DC voltage supply from variable frequency and variable voltage AC power out of the generators. These topologies suffer from bulky and heavy low-frequency tranformer size, lack of DC-link voltage regulation flexibility, high degree of harmonic contents in the input currents, and additional cooling arrangement requirements. This work presents an alternative approach to develop TRUs using actively controlled three-phase AC-DC power factor correction (PFC) rectifiers. This work only focuses on the AC-DC stage of a regulated transformer rectifier unit (RTRU). Three different three-phase topologies i.e. buck-type, boost-type and buck-boost-type are investigated and studied in details in terms of their suitability for TRUs.