1. Dual Switch Flyback Solution
Solution for High Efficiency & Low Standby Power to meet 2013 EuP Computing Product Line Power Conversion Taiwan Fairchild Semiconductor

2. Dual Switch QR Solution
Enabled by
FAN6920 : CRM PFC + QR Controller Combo IC
FAN7382 : HVIC
FAN6204 : Syn. Rectifier IC

3. Basic Operation of Dual Switch Flyback
Phase 1: Q1&Q2 On
Phase 3&4: Q1&Q2 off, D1&D2 off
Phase 2: Q1&Q2 Off, D1, D2 on

4. Benefit of Dual Switch Flyback (1) Snubber and Leakage Inductance Loss Improved
No snubber loss and heat problem
Leakage inductance is recycled into bulk capacitor
Single Flyback
iDS
iLK
Up to 70% of leakage inductance can be recycled
Dual Flyback

5. Benefit of Dual Switch Flyback (2) Low MOSFET Vds and Near ZVS switching
Low MOSFET Drain Source Voltage  Good reliability
Allow large n design  Near ZVS Switching  Low switching loss
Vds = Vin + n*Vo + Spike
Vds= Vin/2
Spike is clamped by two recycle diodes, stress shared by two MOS
Vds of Single Flyback
Larger switching loss
Vds of Dual Flyback
Near ZVS Switching

6. Benefit of Dual Switch Flyback (3) Low VDS of SR MOS for secondary conduction loss
Benefit of high turn ration n to SR MOSFET
VDS of SR MOS is : Vin/n + Vout
Large n  Lower VDS  Lower MOS Ron in lower price  cost & efficiency
Example:
Vin = 420V, Vo = 12V, n= 12
 VDS = 420V/ V = 47V
Could choose 60V or 75V
SR MOSFET

7. Benefit of Dual Switch Flyback (4) Built in two level PFC output for low line efficiency
Two Level PFC output to improve low line efficiency
When AC > 180V  M1 off  PFC Vo = 2.5V x (R1+R2)/R2
When AC < 150V  M1 on  R2//R3  PFC Vo= 2.5V x (R1+R2//R3))/(R2//R3) M1
FAN6920 Block Diagram

8. Benefit of Dual Switch Flyback (5) Deep extended valley switch for light load efficiency
Deep extended valley switch ( up to 12th valley) to allow low operating frequency in light load  Improved light load efficiency
Load ↓ Freq↑
 Poor light load efficiency
Freq. nearly constant
QR Operation without extended valley switch
Other IC: QR Operation with extended valley ( up to 4th valley)
5th valley detect
First valley detect
12th valley detect
FAN6920 Deep extended valley switch

9. Benefit of Dual Switch Flyback (6) Power Saving
Dual Switch Flyback Could Meet < 0.25W ( 2013 EuP)
PFC Stage:
High line/light load  Turn off PFC
Low line/light load  burst mode
QR Stage:
enter into burst mode when light load
No snubber loss
SR Stage:
Turn off SR when light load
Power Saving
Load
VAC
Po = 0 W
Po= 0.25W
115V
0.186W
0.482W
230V
0.195W
0.486W

10. Target Application For Power Range from 75W ~200W All in One PC Power
LED TV
Notebook Adapter
Game Console
LED Lighting

11. Dual-switch Flyback Schematic

12. Solution Comparison Dual Switch QR Flyback LLC Note Efficiency
D2D stage : Nearly ZVS switching
D2D stage: ZVS switching
PFC stage:
Better low line efficiency by two level PFC output
Poor low line efficiency due to high PFC output
LLC could allow only narrow input voltage range
Light load (~20%) :
Higher efficiency due to slow freq. to reduce switching loss
Low efficiency due to high frequency.
FAN6920 could do up to 12th valley detection for slow frequency
Dynamic
Good line transient response
Poor line transient response
Inherent characteristic of topology
Good load transient response
Poor load transient response
Power Saving
<0.3W,
<0.5W,
LLC couldn’t allow PFC turn off at light load.
Design Easiness
Easy
Difficult
Resonant L & C control to prevent ZVS fail
Manufacture Easiness

13. Key Parts Comparison MOSFET 3 (PFC and dual switch) 3 (PFC and LLC)
Transformer
1 for PFC
1 for D2D
1 for resonant L & C IC
FAN6920MR+FAN7382 (HVIC)
CRM PFC+ LLC controller SR
FAN6204
2 SR controller 1
2 MOSFETs
Cost
-Lower transformer cost
-Lower MOSFET cost
-One SR MOSFET needed
-Higher transformer cost
-Might need additional resonant T’mer
-Two SR MOSFET needed
-Might need additional std by stage for power saving
Power Range
75W~200W
100W~500W

14. Dual Switch Flyback vs. LLC
Efficiency: test board 90W/19V
No load

15. Slim Type 19V/ 90W Dual Switch Flyback Efficiency Test Result
Efficiency (18 AWG 1.2m wire include):
No Load Power Consumption:
22.5W
45W
67.5W
90W
115VAC
89.48%
90.54%
90.40%
89.61%
230VAC
91.24%
90.04%
90.86%
90.88%
Input 0.25W
VAC (RMS)
PIN(W)
115
0.482
230
0.486
60mm
95mm
16.5mm

16. 19V/180W Dual Flyback FAN6204 + FDP032N08

17. 130W/19V AIO power 100mm 145mm Efficiency 20% 26W 50% 65W 100% 130W
AIO 130W
Input no load
VAC (RMS)
PIN(W) 90
0.19
115
0.186
230
0.195
264
0.21
Efficiency
20%
26W
50%
65W
100%
130W
3 point
AVG.
115Vac/60Hz
89.29%
92.15%
92.32%
91.25%
230Vac /50Hz
91.65%
93.59%
92.56%
Input 0.25W
VAC (RMS)
PIN(W)
115
0.478
230
0.482
Spec: PIN<0.5W 2013 EUP

18. 200W/19V AIO Power Efficiency 20% 40W 50% 100W 100% 200W 3 point AVG.
Output no load
Output 0.25W
VAC (RMS)
PIN(W) 90
0.168
115
0.183
230
0.206
264
0.223
VAC (RMS)
PIN(W)
115
0.484
230
0.487
Efficiency
20%
40W
50%
100W
100%
200W
3 point
AVG.
115Vac/60Hz
90.01%
91.62%
90.76%
90.79%
230Vac /50Hz
92.16%
91.76%
92.60%
92.17%
Output 0.5W
VAC (RMS)
PIN(W)
115
0.762
230
0.781

19. Example Circuit (19V/90W)

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