®
Design Idea DI-21
TOPSwitch®-GX 45 W, Universal
Input, LCD Monitor External Adapter
Topology
Flyback
Device
Power Output
Input Voltage
Output Voltage
Application
LCD Monitor
45 W
90-265 VAC
TOP247Y
12 V
current limit is further reduced as a function of line voltage
byR4-R6toprovideapproximatelyconstantoverloadpower
vs. line. The larger TOPSwitch-GX selection reduces
conductionlosses,raisingefficiency(withoutcircuitchanges
or increased overload power), and permits a high inductance
design with a small EE30 core for higher efficiency.
Design Highlights
• High efficiency, >82% at 90 VAC
• Low part count solution
• ExtremelylowEMI–frequencyjitterhelpsmeetEN55022B
and FCC B limits with output return grounded
• Low zero load power consumption, <250 mW at 115 VAC
• Line undervoltage detection (UV) and overvoltage (OV)
power system surge protection
Key Design Points
• Differential and common mode surge immunity to
4 kV (EN61000-4-5)
• 100 kHz ring wave immunity to 4 kV (IEEE C62.41)
• Nominal UV and OV set points are calculated according
to the equations:
VUV = (50 µA x R1) + 2.5 V, VOV= (R1 x225 µA) + 2.9 V
• C2 provides high frequency bypass for high voltage DC
bus, reducing high frequency EMI.
• C3 reduces clamp Zener temperature and increases
efficiency. R18 in series with C3 damps drain ringing.
• Ferrite beads, instead of RC snubbers are used on output
rectifier D7 to reduce zero load power consumption.
• L5 and L6 reduce common mode conducted interference
at high frequencies (>10 MHz).
Operation
ThedesigninFigure1utilizestheTOP247Yandtakesadvantage
of many of the device’s features. Line UV and OV (100 V and
450 V, respectively) are implemented using a single 2 MΩ
resistor (R1). Undervoltage eliminates power-up/down output
glitches and overvoltage provides protection for both short
duration transients and long duration power system surges,
removingtheneedforaninputMOV. ResistorR8programsthe
internal current limit of the TOP247Y to 50% of nominal. The
• T1 shield winding (pins 2-3) reduces EMI. R7 damps
ringing caused by shield capacitive currents.
Note: Beads L3 and L4
are placed on D7
anode leads
CY1
2.2 nF
Y1
L6
R18
68 Ω
0.5 W
R7
220 Ω
L2
L3
Bead
1T Through
Ferrite Bead
R4-R6
2.7 MΩ
3.3 µH, 5 A
12 V, 3.75 A
L4
C10
VR1
P6KE
200
D1
D2
Bead
R4
R5
C7, C8
C9
100 nF
T1
D1-D4
680 µF
220 µF
35 V
2
7, 9
RL205
35 V
D7
MBR20100
2 A, 600 V
RTN
F1
10,12
5
3
1
L1
C3
3.15 A
L
10 mH
1.4 A
4.7 nF
1 kV
C1
100 µF
400 V
C2
20 nF
1 kV
CX1
330 nF
X2
R1
2 MΩ
0.5 W
U2
90-265
VAC
C6
1 µF
50 V
D6
D5
UF4005
LTV817A
1N4148
R13
38.3 kΩ
1%
R11
1 kΩ
4
t°
6
N
D
L
R6
TOPSwitch-GX
U1
TOP247Y
RT1
5 Ω, 2.8 A
CONTROL
CONTROL
C
D3
D4
R10
470 Ω
GND
C11
47 nF
R9
S
X
F
6.8 Ω
C4
100 nF
L5
R8
15 kΩ
3T Ground Wire
Through Ferrite Bead
R12
4.7 kΩ
C5
C12
22 µF
25 V
47 µF
10 V
U3
TL431
R14
10 kΩ
1%
PI-3003-051303
Figure 1. TOPSwitch-GX 45 W LCD Monitor Adapter.
May 2003
DI-21
www.powerint.com