1. 12V/5A AC Adapter Demoboard L6565 – Quasi-Resonant Controller Demoboard Performance

2. L6565 – Features Overview

3. L6565 – Block Diagram
Input of the comparator, the outcoming signal depending on the comp and the VFF pin
Current sense input, signal exceeds 2V will make the controller running into hiccup mode.
Error Amplifier feedback input, FB regulate at 2.5V
Output Drive Capability 400mApk
UVLO, Vcc turn-on 13.5V and turn-off 9.5V
Output of the current comparator block,
It will be active when the current signal exceeds 2V
Zero Current Detection
Once detect the negative going edge demag signal, it triggers the MOSFET turn-on.

4. L6565 – Internal Supply Block
Once the Vcc reaches the startup voltage, the controller begins to operate

5. L6565 – Zero Current Detection
Once the demag pin goes down below 1.6V, the EXT MOSFET will be switched on.To ensure high noise immunity, the triggering block must be armed first: prior to falling below 1.6V, the voltage on pin 5 must experience a positive-going edge exceeding 2.1 V.

6. Zero Current Detect Operation

7. Major Parasitic Elements in Flyback Converter
where
Cd is the total capacitance of the drain node
Llk is the leakage inductance of the transformer
Lm is the magnetizing inductance of the transformer

8. VDS Waveform
where
The first valley occurs at T = Tv, where Tv will be as the following
For zero voltage condition, it implies that

9. QR  Timing and Power Relationship
MOSFET ON time:
MOSFET OFF time:
Switching Frequency:
Input Power:
The switching frequency related to input power:
where

10. L6565 – Power Compensation, high line and low line

11. Switching Frequency vs. Operating Condition
In order to deliver the full loading power at minimum input voltage, the inductance should not exceed the following value:

12. Switching Frequency Foldback
The Tblank function is the function of the Vcomp output

13. L6565 – Syn-Rect Demoboard Circuit
QR mode is the perfect topology for syn-rect because secondary current
flow stops before primary MOSFET switches on!

14. Low Startup Circuit
This part is for startup purpose use. The power loss dissipation is much reduced compared with the traditional lossy R-C startup circuit.
The charge current pump into the Vcc capacitor at a rate of

15. Isolation Gate Drive Transformer
L202 – isolated gate drive transformer
The gate drive voltage is converted from the secondary current.
When the secondary current is large enough, it turns on the Q203, then an output voltage is directly going into the totem pole input and drive the secondary MOSFET.
When the secondary current drops to zero, there will be no driving voltage from the isolated gate drive transformer, and Q203 turn-off and the MOSFET will not turn on.
Secondary current
Isolated gate drive transformer
Make use of syn-rect approach, efficiency improves significantly!

16. Operating Waveforms Vin = 240Vac, Vo=12.3V and Io=5A
Primary current
Vdrain
Vin = 100Vac, Vo=12.3V and Io=5A
Primary current
Vdrain
Vin = 240Vac, Vo=12.3V and Io=5A

17. Operating Waveforms Vin = 100Vac, Vo=12.3V and Io=5A
Primary current
Primary current
Vdrain
Vdrain
Vin = 100Vac, Vo=12.3V and Io=5A
Vin = 240Vac, Output Short Circuit

18. Transformer Design (I)

19. Transformer Design (II)
In Quasi-Resonant mode control, the current always starting from zero of every switching cycle. 

20. Syn-Rect Demoboard Transformer
Np: 520uH

21. Syn-Rect Demoboard Full Load Efficiency

22. No Load Input Power

23. Demoboard BOM Item Reference Part Description 1 Assembly Dwg. 2
Schemaitc 3
PC Board
PC Board,1-Layers,60mm x118mm 4
F101
3A/250V
fuse 5 RT
9D-207 6 RV
G471
varistor 7
R101
15ohm
resistor 8
R102
100K
3W resistor 9
R104
10ohm 10
R105 11
R106 3M 12
R107
16K 13
R108A,R108B
510K 14
R110
47K 15
R201,R203 1K 16
R202
100ohm 17
R204
470ohm

24. Demoboard BOM 18 R207 5.1K resistor 19 R208 20K 20 RS101 0.33ohm
3W resistor 21
CX101
0.22UF/275V
X2 cap 22
C101
1nF/1KV
capacitor 23
C102
150U/400V
Ecap 24
C103
220U/25V 25
C104
10nF/50V 26
C105,C205
1nF/50V 27
C106
56nF/400V 28
C201,C202,C203
1000uF/25V 29
C204
470U/25V 30
C206
6.8nF/63V 31
C207
100nF/50V 32 CY
222U/275V
Y1 cap 33
BR101
KBU406
bridge rectifier 34
D101,D102,D201
1N4148
diode

25. Demoboard BOM 35 D103 clamper diode diode 36 D104 FR107 37 Q101
STP10NK60Z
MOSFET 38
Q201
STP1806 39
Q202,Q203
2N3904
transistor 40
Q204
2N3906 41
Q205
TL431
voltage reference 42
L101 共模
common mode choke 43
L102 44
L201 差模
differential mode choke 45
L202
感应磁环
gate drive transformer 46
OPT
K817P6
opto-coupler 47
IC101
L6565
SO8 48
TR1
Transformer
transformer