Noise Generation in a Forward DC-to-DC Converter

The mechanism of switching-noise generation is examined for the most popular power converter, i.e. the forward dc-to-dc converter. Particularly the output noise voltage generated during the transistor's turnoff is analyzed by dividing the turnoff time into four sequent states and deriving the corresponding high-frequency equivalent circuits. In these circuits the parameter of transistor's fall time is also introduced. As the result, not only the influence of the inductive or capacitive parasitic elements on the noise generation but also the relationship between the transistor's switching speed and the noise voltage are quantitatively clarified.