AN-6920MR Datasheet, PDF (1/17 Pages) Fairchild Semiconductor – Integrated Critical-Mode PFC / Quasi-Resonant Current-Mode PWM Controller FAN6920

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AN-6920MR
Integrated Critical-Mode PFC / Quasi-Resonant
Current-Mode PWM Controller FAN6920
1. Introduction
This application note presents practical step-by-step design
considerations for a power supply system employing
Fairchild’s FAN6920 PFC / PWM combination controller,
an integrated Boundary Conduction Mode (BCM) Power
Factor Correction (PFC) controller and Quasi-Resonant
(QR) PWM controller. Figure 1 shows the typical
application circuit, where the BCM PFC converter is in the
front end and the dual-switch quasi-resonant flyback
converter is in the back end.
FAN6920 achieves high efficiency with relatively low cost
for 75~200W applications where BCM and QR operation
with a two-switch flyback provides best performance. A
BCM boost PFC converter can achieve better efficiency
with lower cost than continuous conduction mode (CCM)
boost PFC converter. These benefits result from the
elimination of the reverse-recovery losses of the boost diode
and zero-voltage switching (ZVS) or near ZVS (also called
valley switching) of boost switch. The dual-switch QR
flyback converter for the DC/DC conversion achieves
higher efficiency than the conventional flyback converter
with leakage inductor energy recycles.
The FAN7382, a monolithic high- and low-side gate-driver
IC, can drive MOSFETs that operate up to +600V.
Efficiency can be further improved by using synchronous
rectification in the secondary side instead of a conventional
rectifier diode.
Figure 1. Typical Application Circuit
© 2010 Fairchild Semiconductor Corporation
Rev. 1.0.0 • March 10, 2011
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