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.