Very high efficiency techniques and their selective application to the design of a 70 A rectifier

Latest techniques for the design and construction of high efficiency, high performance switched mode power supplies are investigated, compared with older techniques, and implemented in the optimised design of a 70 A, 54 VDC telecommunications rectifier which draws unity power factor from the AC supply while exceeding 93% conversion efficiency. A new `lossless´ snubber is introduced which combines di/dt and dv/dt limiting properties to greatly improve efficiency while using 30% fewer parts than conventional `lossy´ snubbers. Another novel approach used is the parallel combination of IGBT and MOSFET to form a hybrid power switch with a very low on-voltage and a low turn-off loss. Contrary to popular trends the switching frequency is kept low to minimise switching losses. The combination of these techniques and others discussed in the paper, yields a unit with excellent efficiency and some advantages which further benefit both manufacturer and end user