Optimal selection of bulk capacitors in flyback converter

Review, Properties, and Synthesis of Single-Switch Non-Isolated DC-DC Converters with a Wide Conversion Range

“…Considering that all converters in Figure 3 operate in CCM, the voltage gains of the N-stage cascaded buck, boost, and buck-boost converters are given by ( 6)- (8), respectively.…”

“…where D1… DN are the duty ratios associated with active switches S1…SN, respectively; N is the number of cascaded converters; and n = 1, 2, … N corresponds to a given stage. It i also noteworthy that "+" and "−" in (8) denote that the output voltage is positive or nega tive, respectively. This concept can also be applied in the cascade connection of distinct topologies, suc as the two-stage association represented in Figure 4, in which a buck converter follows buck-boost one.…”

“…In turn, incorporating high-frequency transformers can extend the voltage conversion ratio of DC-DC converters [7]. The classical isolated topologies, such as the flyback, forward, push-pull, half-bridge, and full-bridge converters, allow for adjusting the output voltage according to not only the duty cycle but also the transformer turns ratio, aiming to achieve high step-up or high step-down [8]. Since high-frequency transformers rely on materials with high magnetic permeability, such as ferrite, unlike their low-frequency counterparts based on silicon-steel, they may be limited in size due to the lack of mechanical robustness and ability to process power levels up to 50 kW; this being a conservative estimate according to [9].…”