Analysis of surge and noise generation mechanism in a forward DC‐to‐DC‐converter

The surge and noise generation in a switching converter depends heavily on the switching speed of the transistor, the recovery characteristics of the diode, the leakage inductances of the transformer and other parasitic inductances, and capacitances. Therefore its mechanism is so complicated that to obtain a complete understanding of the mechanism of surge and noise generation, it is definitely necessary to introduce the analytical procedure through which the quantitative discussions are made. This paper clarifies the mechanism of surge and noise generation in a forward dc-to-dc converter which is one of the most popular types of converter. The analysis is performed by partitioning the switching time into several states and deriving a high-frequency equivalent circuit for each state. The equivalent circuits include not only inductive and capacitive parasitic parameters, but also the parameters related to the switching speed of the transistor and the recovery characteristics of the diode. As a result, the effects of these various parameters on the surge and noise generation are clarified quantitatively.