| Abstract |
BIFRED and BIBRED are Single-Stage Power Factor Correction converters. The converters have one
active switching stage, which is used to shape the input current and to regulate the isolated output
voltage. However, leakage inductance of the transformers in BIFRED or BIBRED causes a high
voltage over the switching device at turn-off instant of the switch. In these two converters the problem
associated to the leakage inductance is more severe than in more traditional power supply topologies.
This is because the current of the transformer, and hence the current of the leakage inductance, have to
be changed from a high positive value to a high negative value during a short period of time, rather
than to merely suppress the current to zero after the switch has been turned off. A large change in the
inductive current requires that a relatively high voltage have to be applied across the inductance. A
snubber circuit has to be employed to provide the needed voltage and to provide an alternative path for
the currents for the duration of the process of changing the direction of the current. This paper will
give a detailed analysis of a lossless snubber in the BIFRED and BIBRED circuits. Especially the
turn-off transition is analyzed in detail since this mode of operation differs from the corresponding
transition of other power supply topologies. Simulated results presented in the paper will verify the
analysis. |
