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Design of a Two-Switch Flyback Power Supply Using 1.7 kV SiC Devices for Ultra-Wide Input-Voltage Range Applications

Wire diagram of a flyback converter with two switches and the implemented gate driver
Fig. 1. Two-switch flyback schematic and gate drivers implementation
This paper presents the design and evaluation of a two-switch flyback power supply with an ultra-wide input voltage range (230 - 1300 V), fed from the floating dc bus of power electronics building blocks (PEBB) in medium voltage (MV) modular multilevel converter (MMC) applications. Rated at 80 W, 48 V output, and operating at 50 kHz, the proposed converter uses 1.7 kV SiC devices and a planar PCB winding transformer to achieve a low-profile form factor. Further, a pre-charge circuit and start-up sequence are developed as well, enabling the two switch flyback converter to wake up at 230 V, as shown in fig 2. Experimental results are presented for verification and evaluation purposes.

The two-switch flyback topology provides the best trade-off in terms of performance and complexity among other topologies like LLC or full-bridge. With reference to Fig. 1, the benefit of this topology is that the over-voltages on the power switches are clamped to the dc bus by diodes D1 and D2, thus allowing the use of power switches with a breakdown voltage of 1.5 kV. Since this circuit topology is basically hard-switching, SiC MOSFETs (CREE C2M-1000170D 1.7 kV/5 A) have been chosen to reduce the losses of Q1 and Q2. Another feature of the two-switch flyback converter is that during the clamping period the leakage energy of the transformer is returned back to the source, effectively eliminating the need for dissipative snubber circuits.

Picture of the completed circuit board both from the side and top. The completed board shows the total length is that of a standard mechanical pencil, and the width is smaller.
Fig. 2. Picture of PEBB prototype (a) top view (b) side view
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