AN-9732 Datasheet, PDF (1/22 Pages) Fairchild Semiconductor – LED Application Design Guide Using BCM Power Factor Correction (PFC) Controller for 200W Lighting System

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AN-9732
LED Application Design Guide Using BCM Power Factor
Correction (PFC) Controller for 200W Lighting System
1. Introduction
This application note presents practical step-by-step design
considerations for a Boundary-Conduction-Mode (BCM)
Power-Factor-Correction (PFC) converter employing
Fairchild PFC controller, FL7930. It includes designing the
inductor and Zero-Current-Detection (ZCD) circuit,
selecting the components, and closing the control loop. The
design procedure is verified through an experimental 200W
prototype converter.
Unlike the Continuous Conduction Mode (CCM) technique
often used at this power level, BCM offers inherent zero-
current switching of the boost diodes (no reverse-recovery
losses), which permits the use of less expensive diodes
without sacrificing efficiency.
The FL3930B provides an additional OVP pin that can be
used to shut down the boost power stage when output
voltage exceeds OVP level due to damaged resistors
connected at the INV pin. The FL7930C provides a PFC-
ready pin can be used to trigger other power stages when
PFC output voltage reaches the proper level (with
hysteresis). This signal can be used as the V_CC trigger signal
for another power stage controller after PFC stage or be
transferred to the secondary side to synchronize the
operation with PFC voltage condition. This simplifies the
external circuit around the PFC controller and saves total
BOM cost. The internal proprietary logic for detecting input
voltage greatly improves the stability of PFC operation.
Together with the maximum switching frequency clamping
at 300KHz. FL7930 can limit inductor current within pre-
designed value at one or two cycles of the AC-input-absent
test to simulate a sudden blackout. Due to the startup-
without-overshoot design, audible noise from repetitive
OVP triggering is eliminated. Protection functions include
output over-voltage, over-current, open-feedback, and
under-voltage lockout.
An Excel^®-based design tool is available with this
application note and the design result is shown with the
calculation results as an example.
© 2011 Fairchild Semiconductor Corporation
Rev. 1.0.0 • 3/23/11
Figure 1. Typical Application Circuit
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