1. Synchronous Rectifier in Forward Converter

2. Synchronous Rectifier
Rectifier Circuit
Rectifier Concept
Synchronous Rectifier
C -1 : RCD Clamp & Self - Driven SRs
C -2 : Active Clamp & Self - Driven SRs
C -3 : Control – Driven
D. Power Loss Comparisons
E. Efficiency Curve

3. A. Rectifier Circuit Fig1 : Forward Converter with MOSFET
Fig2 : Forward Converter with Diode

4. B. Rectifier Concept
The switching losses caused by the reverse recovery current of the body - diode will be dependent of the carried current in the instant in the which the voltage between anode and cathode reverses become negative

5. C. Synchronous Rectifier
C-1 RCD Clamp & Self – Driven SRs
Gate –Driver signal
Drain to Source voltage of primary switch
Secondary winding voltage
Current through SR2
Current through SR3

6. C. Synchronous Rectifier
C-2 Active Clamp & Self – Driven SRs
Gate –Driver signal
Drain to Source voltage of primary switch
Secondary winding voltage
Current through SR2
Current through SR3

7. C. Synchronous Rectifier
C-3 Control – Driven SRs
Gate –Driver signal
Drain to Source voltage of primary switch
Secondary winding voltage
Current through SR2
Current through SR3

8. D. Power Loss Comparisons
Converter efficiency
Converter Efficiency
( For Schottky Rectifiers )
( For Synchronous Rectifiers )
PO : Output Power Ploss : Total Loss ;
PSH : Schottky Rectifiers Loss PSR : Synchronous Rectifiers Loss

9. D. Power Loss Comparisons
Schottky Power Loss
Self – Drivens SR Loss
Control – Drivens SR Loss

10. D. Power Loss Comparisons
Efficiency
( RCD Self –Driven SRs)
Efficiency
( Active Self –Driven SRs)
Efficiency
( Control –Driven SRs)
VD = VSH = Body Diode Voltage ; Ddead = dead time duty cycle ; Ddelay = delay time duty cycle

11. E. Efficiency Curve
Ddelay ≈ 0

12. E. Efficiency Curve
Ddead ≈ 0.2