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A technique to achieve an efficient and low cost unity power factor for a three-phase controlled rectifier is described. The proposed technique can be used to retrofit a variety of thyristor converters for various applications. It consists of a thyristor bridge, three bidirectional switches, and a current shaping network. The bidirectional switches are turned on at double the line frequency of 50 Hz. Its current shaping network is very simple and consists of only two capacitors and three resistors. The scheme provides a simple, light, fast and economical upgrading to the existing controlled rectifier-based DC drives. In general, it is also suitable for medium to high power AC-DC converters used in UPS, HVDC, etc.