Backward-Noise Generation in Forward DC-to-DC Converters

The generation mechanism of backward noise is analyzed for a forward dc-to-dc converter. Here the backward noise is defined as the noise which flows back to the input terminals due to the switching mechanism itself as opposed to powerline conducted emissions related to harmonics of the ideal switching waveforms. Its generation process consists of several states, and there are two modes depending on the characteristics of the switching elements used in the converter. The analysis is performed by deriving the high-frequency equivalent circuit corresponding to each state. The equivalent circuits include the parameters associated with the switching speed of a transistor and the recovery characteristics of a diode, as well as inductive and capacitive parasitic parameters. As the result, the effects of these parameters on the backward noise are made clear quantitatively.