A special buck-boost converter

A special step-up/down converter is investigated. The basic function, the stationary relationships, the small signal behavior, the position of the poles and zeros and the dimensioning are discussed. For a model converter, simulation and measurement results are compared. The advantages of this converter are: the duty ratio is always larger than 0.5 giving, an easier realization of a low-loss snubber circuit and therefore making higher switching frequencies possible; an equal voltage is given across the two inductors, making a coupling possible and therefore a realization on a common core; the control of the active switch does not have to be floating. Because the circuit has some serious disadvantage, the advantages can take effect only for special and limited applications. Such disadvantages are: pulsed current drawn from the source; for larger duty ratios substantially higher currents than the load current flow in the semiconductor devices and in the input inductor. This results in high conduction losses in the semiconductors, relatively low efficiency and problems with cooling.<
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