AN-6206

Part No.:
AN-6206
Download:
Download
Description:
Primary-Side Synchronous Rectifier (SR) Trigger Solution for Dual-Forward Converter
File Size:
546 K
Page:
9 Pages
Logo:
Maker:
FAIRCHILD [ FAIRCHILD SEMICONDUCTOR ]
PCB Prototype

July 19, 2018:

ANT016008LCD1575MA1

AOD417

AOL1448

AP5004SG-U

APTGF75DH120TG

ASC-5S15D

ASMT-RA45-AP932

ASX602

ATM0350D21

ATS045045021-SF-15T

AW2204

AWT6302RM9Q7

PCB Datasheet:1PCB Datasheet:1
www.fairchildsemi.com
AN-6206
Primary-Side Synchronous Rectifier (SR) Trigger Solution
for Dual-Forward Converter
Introduction
In any switching converter, rectifier diodes are used to
obtain DC output voltage. The conduction loss of diode
rectifier contributes significantly to the overall power losses
in a power supply; especially in low output voltage
applications, such as personal computer (PC) power
supplies. The conduction loss of a rectifier is proportional to
the product of its forward-voltage drop and the forward
conduction current. Using synchronous rectification (SR)
where the rectifier diode is replaced by MOSFET with
proper on resistance (Rds
ON
), the forward-voltage drop of a
synchronous rectifier can be lower than that of a diode
rectifier and, consequently, the rectifier conduction loss can
be reduced.
The highly integrated FAN6210 is a primary-side SR
controller for dual-forward converter that provides control
signals for the secondary-side SR driver FAN6206.
FAN6210 also provides drive signal for the primary-side
power switches by using an output signal from the PWM
controller. FAN6210 can be combined with any PWM
controller that can drive a dual-forward converter. To obtain
optimal timing for the SR drive signals, transformer winding
voltage is also monitored. To improve light-load efficiency,
green-mode operation is employed, which disables the SR
turn-on trigger signal, minimizing gate drive power
consumption at light-load condition.
This application note describes the design procedure of SR
circuit using FAN6210 and FAN6206. The guidelines for
printed circuit board (PCB) layout and a design example
with experiment results are also presented.
V
in
V
ac
PFC stage
C
bulk
Drv
L
o
n:1
R
8
Q
2
D
1
V
o
FAN6210
1 XP
2 XN
PWM control signal
(From PWM controller)
3 SIN
GND 8
SOUT 7
VDD 6
Q
1
R
2
Drv
R
9
R
6
R
7
FAN6206
4 RDLY DET 5
R
1
D
5
D
6
D
3
D
4
C
1
D
2
From power supply
of PWM controller
1 LPC1GATE1 8
2 LPC2 GND 7
R
3
R
4
R
5
PT
3 SN
4 SP
GATE2 6
VDD 5
C
2
Figure 1. Typical Application
© 2010 Fairchild Semiconductor Corporation
Rev. 1.0.0 • 4/27/10
www.fairchildsemi.com