AN4146 Datasheet, PDF (1/24 Pages) Fairchild Semiconductor – Design Guidelines for Quasi-Resonant Converters

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Application Note AN4146
Design Guidelines for Quasi-Resonant Converters
Using FSCQ-series Fairchild Power Switch (FPS^TM)
Abstract
In general, a Quasi-Resonant Converter (QRC) shows lower
EMI and higher power conversion efficiency compared to
the conventional hard switched converter with a fixed
switching frequency. Therefore, it is well suited for color TV
applications that are noise sensitive. This application note
presents practical design considerations of Quasi-Resonant
Converters for color TV applications employing FSCQ-
series FPS^TM (Fairchild Power Switch). It includes
designing the transformer, output filter and sync network,
selecting the components and closing the feedback loop. The
step-by-step design procedure described in this application
note will help engineers design Quasi-Resonant Converter
easily. To make the design process more efficient, a software
design tool, FPS design assistant which contains all the
equations described in this application note, is also provided.
The design procedure is verified through an experimental
prototype converter.
D_R(n)
L_P(n)
N_S(n)
C_O(n)
C_P(n)
N_p
D_R1
L_P1
AC
N_S1
IN
C_O1
C_P1
FSCQ-series
Drain
V_O(n)
V_O1 (B+)
Sync
PWM
Cr
GND
V_FB
C_B
Vcc
R_{cc Vco Da}
D_zc
C_{a1 Ca2}
N_a
D_SY
R_str
R_SY1
D_R2
N_S2
C_O2
R_d
H11A817A
C_SY
R_SY2
KA431
L_P2
C_P2
R_bias
R₁
R_F
C_F
V_O2 (Sound)
Linear
regulator
MCU
R₃
Dz
R₁
R₂
Q
Picture ON
Figure 1. Basic Quasi-Resonant Converter (QRC) Using FPS (Color TV Application)
1. Introduction
The FSCQ-series FPS^TM (Fairchild Power Switch) is an
integrated Pulse Width Modulation (PWM) controller and
Sense FET specifically designed for Quasi-resonant off-line
Switch Mode Power Supplies (SMPS) with minimal external
components. Compared with discrete MOSFET and PWM
controller solution, it can reduce total cost, component count,
©2005 Fairchild Semiconductor Corporation
size and weight, while simultaneously increasing efficiency,
productivity, and system reliability.
Figure 1 shows the basic schematic of an FPS based Quasi-
Resonant Converter for the color TV application, which also
serves as the reference circuit for the design process
described in this application note. An experimental converter
from the design example has been built and tested to show
the validity of the design procedure.
Rev. 1.0.1