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12V/5A AC Adapter Demoboard
L6565 – Quasi-Resonant Controller
Demoboard Performance
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L6565 – Features Overview
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L6565 – Block Diagram
Zero Current Detection
Once detect the negative going edge demag signal, it triggers the MO
SFET turn-on.
Output Drive Capability 400mApk
Error Amplifier feedback input, FB regulate at
2.5V
Current sense input, signal exceeds 2V
will make the controller running into hiccup mode.
Input of the comparator, the outcoming signal depending on the comp and the VFF pin
UVLO, Vcc turn-on 13.5V and turn-off 9.5V
Output of the current compara
tor block,
It will be active when the current signal excee
ds 2V
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L6565 – Internal Supply Block
Once the Vcc reaches the startup voltage, the controller b
egins to operate
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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.
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Zero Current Detect Operation
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Major Parasitic Elements in Flyback Converter
whereCd is the total capacitance of the drain nodeLlk is the leakage inductance of the transformerLm is the magnetizing inductance of the transformer
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VDS Waveform
The first valley occurs at T = Tv, where Tv will be as the following
For zero voltage condition, it implies that
where
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QR Timing and Power Relationship
MOSFET ON time:
MOSFET OFF time:
Switching Frequency:
Input Power:
The switching frequency related to input power:
where
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L6565 – Power Compensation, high line and low line
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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:
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Switching Frequency Foldback
The Tblank function is the function of the Vcomp output
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L6565 – Syn-Rect Demoboard Circuit
QR mode is the perfect topology for syn-rect because secondary current
flow stops before primary MOSFET switches on!
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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 .
ac
acstart
f
VC
2
2
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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.
Isolated gate drive transformer
Secondary current
Make use of syn-rect approach, efficiency improves significantly!
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Operating Waveforms
Primary current
Vdrain
Vin = 100Vac, Vo=12.3V and Io=5A
Primary current
Vdrain
Vin = 240Vac, Vo=12.3V and Io=5A
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Operating Waveforms
Vin = 240Vac, Output Short Circuit
Primary current
Vdrain
Vin = 100Vac, Vo=12.3V and Io=5A
Primary current
Vdrain
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Transformer Design (I)
in
pkpon V
ILT
voffon TTTfsw
1
R
pkpoff V
ILT
dpv CLT
2
minmax
minmax
max
112
1
dswRin
swin
p
CfVV
fP
L
Calculation Worksheet -- Primary InductanceParameters Value Lp 4.59E-04 Ipk 2.469034416
Pin 70
Fsw 50000 where Lp is the primary inductance
Vin 100 Fsw is the Switching Frequency
Vr 142 Vin is the minimum input voltage
Cd 1.00E-10 Cd is the equivalent output drain to source capacitance
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Transformer Design (II)
ep
p
AN
ILB
Calculation Worksheet - Magnetic Flux DensityParameters Value
ΔB 0.25 ΔB is the magnetic flux density
Δ I 2.34 Δ I is the change of current
Np 3.43E+01 Np is the primary inductance
Ae 1.42E-04 Ae is the effective area of the magnetics
Lp 5.20E-04 Lp is the primary inductance
In Quasi-Resonant mode control, the current always starting from zero of every switching cycle.
pkII
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Syn-Rect Demoboard Transformer
Np: 520uH
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Syn-Rect DemoboardFull Load Efficiency
Efficiency
0. 00
10. 00
20. 00
30. 00
40. 00
50. 00
60. 00
70. 00
80. 00
90. 00
100. 00
Input Voltage(V)
Eff
icie
ncy
%
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No Load Input Power
No Load Power Loss
0. 00
100. 00
200. 00
300. 00
400. 00
500. 00
600. 00
700. 00
800. 00
900. 00
1000. 00
100
110
120
130
140
150
160
170
180
190
200
210
220
230
240
Input Voltage(V)
No
Lo
ad
Po
wer
Lo
ss(
mW)
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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 resistor
10 R105 15ohm resistor
11 R106 3M resistor
12 R107 16K resistor
13 R108A,R108B 510K resistor
14 R110 47K resistor
15 R201,R203 1K resistor
16 R202 100ohm resistor
17 R204 470ohm resistor
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Demoboard BOM
18 R207 5.1K resistor
19 R208 20K resistor
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 capacitor
25 C104 10nF/50V capacitor
26 C105,C205 1nF/50V capacitor
27 C106 56nF/400V capacitor
28 C201,C202,C203 1000uF/25V Ecap
29 C204 470U/25V Ecap
30 C206 6.8nF/63V capacitor
31 C207 100nF/50V capacitor
32 CY 222U/275V Y1 cap
33 BR101 KBU406 bridge rectifier
34 D101,D102,D201 1N4148 diode
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Demoboard BOM
35 D103 clamper diode diode
36 D104 FR107 diode
37 Q101 STP10NK60Z MOSFET
38 Q201 STP1806 MOSFET
39 Q202,Q203 2N3904 transistor
40 Q204 2N3906 transistor
41 Q205 TL431 voltage reference
42 L101 共模 common mode choke
43 L102 共模 common mode choke
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