Design Idea DI-22
®
TOPSwitch-GX
70 W, 19 V
External Laptop Adapter
Application
Laptop Adapter
Device
TOP249Y
Power Output
70 W
Input Voltage
85-265 VAC
Output Voltage
19 V
Topology
Flyback
®
Design Highlights
• High efficiency: 84% at 85 VAC (with 50 ˚C external
ambient temperature)
• Low component count and high power density, 7 W/in.
3
• Very compact design (4.1 in.
×
2.225 in.
×
1.06 in.)
• No surface mount components required
• Low zero load power consumption, <370 mW at 115 VAC
• Approximately constant overload power with line voltage
• Line undervoltage detection (UV) and overvoltage (OV)
shutdown
• Low EMI - switching frequency jitter helps meet CISPR22B/
EN55022B limits
• Fully protected for overload, short circuit and thermal faults
Operation
The design utilizes a TOP249Y in a flyback converter
providing a 70 W output in a sealed enclosure at an external
ambient of 50 ˚C. Line UV and OV (100 V and 450 V,
respectively) are implemented using a single 2 MΩ resistor
(R1). Undervoltage eliminates power-up/down glitches and
overvoltage provides line transient and long duration power
system surge protection. Resistor R10 programs the internal
current limit to 75% of nominal at the UV threshold. As a
function of input voltage the current limit is further reduced
by R9 to provide approximately constant overload power.
The larger
TOPSwitch-GX
selection reduces conduction
losses, raising efficiency (without circuit changes or increased
overload power) and permits a higher inductance design for
reduced primary RMS currents, further increasing efficiency.
D2
MBR20100
C13
C12
C11
0.33
µF
0.022
µF
0.01
µF
400 V
400 V
400 V
C7 2.2 nF
Y1 Safety
1
2
9
VR1
P6KE-
200
2
BR1
RS805
8 A 600 V
D1
UF4006
3
D3
MBR20100
C3
820
µF
25 V
L1
200
µH
C14
0.1
µF
50 V
19 V, 3.6 A
RTN
11
8
L2
820
µH
2A
C6
0.1
µF
X2
C1
150
µF
400 V
D
R11
2 MΩ
1/2 W
T1
D4
1N4148
6
5
C2
820
µF
25 V
U2
PC817A
R1
270
Ω
R8
4.7
Ω
C4
820
µF
25 V
R4
31.6 kΩ
1%
R2
1 kΩ
R13
562
Ω
C9
1%
4.7 nF 50 V
C10
0.1
µF
50 V
R6
4.75 kΩ
1%
PI-2691-033001
RT1
10
Ω
1.7 A
F1
3.15 A
t°
L3
75
µH
2A
R9
13 MΩ
S
C15
TOPSwitch-GX
1
µF
L
50 V
TOP249Y
CONTROL
U1
C
X
F
R3
6.8
Ω
C5
47
µF
16 V
R10
20.5 kΩ
C8
0.1
µF
50 V
U3
TL431
R7
56 kΩ
85-265 VAC
Figure 1. TOPSwitch-GX 70 W Laptop Adapter Schematic.
DI-22
www.powerint.com
September 2002
DI-22
To reduce winding and diode dissipation the secondary is split
into two windings and diode OR’ed into the output capacitors
(C2, 3). Regulation is provided by a secondary side reference
(U3), the output voltage sensed by R4, R13 and R6.
TRANSFORMER PARAMETERS
Core Material
Bobbin
FPQ26/20-A
2
TDK PC40 gappped for A
LG
= 843 nH/T
TDK BPQ26/20-1112CP
Primary: 9T + 9T, 2 x 26 AWG
Shield: 1T, 8 mm x 0.015 mm Cu foil
Secondary 1: 3T, 3 x 26 AWG T.I.W.
Secondary 2: 3T, 3 x 26 AWG T.I.W.
Bias: 2T, 8 mm x 0.015 mm Cu foil
(T.I.W. = Triple Insulated Wire)
Primary (2-1), Shield (1-NC),
tape, Secondary 1 (12-9),
Secondary 2 (11-8),
Bias (6-5), tape, Primary (3-2), tape
Primary: 273
µH ±
10%,
Leakge: 3
µH
(maximum)
1.5 MHz (minimum)
Key Design Points
• D1 and VR1 clamp leakage inductance spikes. A Zener
clamp provides lower zero load consumption than an RCD
clamp and higher efficiency below full load.
• C11 reduces VR1 dissipation, raising efficiency.
• Additional differential filtering is provided by C13 and L3.
• C12 provides high frequency bypass, reducing high
frequency EMI.
• Use foil windings to reduce dissipation and reduce leakage
inductance.
• Sandwich secondary winding between two halves of
primary to reduce leakage inductance.
• High core temperature reduces saturation flux density.
Keep flux density below 3000 gauss (0.3 T) to prevent
saturation.
• Use 100 V Schottky diodes for highest efficiency.
• Good layout practices should be followed:
- Locate C8, R3, C5, R9, R10 and R11 close to U1.
- Power and signal source currents should be separated,
joined using a Kelvin connection at the SOURCE pin.
- Minimize the primary and secondary loop areas to reduce
parasitic leakage and EMI.
• Consult DAK-11 and EPR-11 for more information.
Winding Details
Winding Order
(Pin Numbers)
Inductance
Primary Resonant
Frequency
Table 1. Transformer Construction Information.
For the latest updates, visit our Web site:
www.powerint.com
Power Integrations reserves the right to make changes to its products at any time to improve reliability or manufacturability.
Power Integrations does not assume any liability arising from the use of any device or circuit described herein, nor does it convey any
license under its patent rights or the rights of others.
The products and applications illustrated herein may be covered by one or more U.S. and foreign patents or potentially by pending U.S.
and foreign patent applications assigned to Power Integrations. A complete list of Power Integrations’ patents may be found at
www.powerint.com.
The PI Logo,
TOPSwitch
,
TinySwitch
and
EcoSmart
are registered trademarks of Power Integrations, Inc.
PI Expert
is a trademark of Power Integrations, Inc. ©Copyright 2002, Power Integrations, Inc.
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A
9/02
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