Voltage Sharing Between MOSFETs in a SiC-Based Two-Switch Flyback

The two-switch flyback converter is a variant of the widely used single-switch flyback converter with an additional switch and clamping diodes that limit the peak voltage across each switch to the input DC voltage level. Moreover, the total voltage during the OFF state of the converter operation is divided across two switches, allowing for higher DC input voltages or the use of components with lower voltage ratings. However, contrary to the literature, the voltage is not evenly shared between the series-connected switches on a SiC MOSFET-based two-switch flyback. This imbalance is heavily affected by the capacitive characteristics of the pulse transformer, which is often used to achieve floating gate drive. In this work, the effect is thoroughly analyzed using mathematical and simulation models, and the results are verified with a physical converter prototype. The interwinding capacitance of the pulse transformer was found to have a substantial effect on voltage sharing between MOSFETs.