Analysis of surge and noise generation in a forward dc-to-dc converter

Switching surge and noise voltages are analyzed under the common-mode condition in a forward dc-to-dc converter, which is the most popular converter. The analysis is performed by partitioning the switching time into several states and introducing the high-frequency equivalent circuit corresponding to each state. The equivalent circuits include not only inductive or capacitive parameters but also the parameters related to the transistor´s switching speed and the diode´s recovery characteristics. As a result the effects of these various parameters on the surge and noise generation are made clear quantitatively. Particularly an important feature of the relationship between the transistor´s switching speed and the surge and noise voltages is obtained.