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AN6-206

Fairchild Semiconductor
Part Number AN6-206
Manufacturer Fairchild Semiconductor
Description Primary-Side Synchronous Rectifier (SR) Trigger Solution
Published Apr 1, 2014
Detailed Description www.fairchildsemi.com AN-6206 Primary-Side Synchronous Rectifier (SR) Trigger Solution for Dual-Forward Converter Intro...
Datasheet PDF File AN6-206 PDF File

AN6-206
AN6-206

Overview
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 (RdsON), 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.
Vin Vac PFC stage Cbulk Drv Lo n:1 R8 Q2 D1 Vo FAN6210 1 XP 2 XN PWM control signal (From PWM controller) 3 SIN GND 8 SOUT 7 VDD 6 Q1 R2 Drv R9 R6 R7 FAN6206 4 RDLY DET 5 R1 D5 D6 D3 D4 C1 D2 From power supply of PWM controller 1 LPC1GATE1 8 2 LPC2 GND 7 R3 R4 R5 PT 3 SN 4 SP GATE2 6 VDD 5 ...


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