Linear circuit models of PWM flyback and buck/boost converters

A method for modeling PWM converters operating in continuous conduction mode (CCM) is introduced. First, static voltage and current transfer functions of the idealized switching part of the converters are found. Second, the linearization of these transfer functions at the operating point is carried out, and the idealized switching part is replaced by dependent current and voltage sources. Third, the equivalent average resistance of parasitic resistances and equivalent average voltage of offset voltage sources of switches are determined using the principle of energy conservation. The method leads to linear DC and small-signal circuit models of a PWM converter. To illustrate the method, the analysis of the PWM flyback converter is given. Design equations for DC voltage transfer function, efficiency, and small-signal characteristics are derived.<
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