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
POWERINT [ POWER INTEGRATIONS, INC. ]
