CCM-BOOST Datasheet, PDF (11/18 Pages) Infineon Technologies AG – CCM PFC Boost Converter Design

CCM PFC Boost Converter Design
Turn-off time and loss:
Design Note DN 2013-01
V1.0 January 2013
(11)
(12)
This is the “classic” format for calculating turn-off time and loss; due to the high Q_oss of SJ MOSFETs, the
C_oss acts like a nonlinear capacitive snubber, and actual turn-off losses with fast switching can be up to 50%
lower than calculated. The current flow through the drain during turn-off under these conditions is non-
dissipative capacitive current, and with fast drive, the channel may be completely turned off by the onset of
drain voltage rise.
Output capacitance C_oss switching loss:
(13)
Gate drive loss:
(14)
Boost Diode
Selection of the boost diode is a major design decision in CCM boost, since the diode is hard commutated at
a high current, and reverse recovery can cause significant power loss, noise and current spikes. Reverse
recovery can be a bottle neck for high switching frequency and high power density power supplies.
Additionally, at low line, the available diode conduction duty cycle is quite low, and the forward current quite
high in proportion to the average current. For that reason, the first criteria for selecting a diode in CCM boost
are fast recovery with low reverse recovery charge, followed by V_F operating at high forward current.
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