Design Idea DI-21
®
TOPSwitch-GX
45 W, Universal
Input, LCD Monitor External Adapter
Application
LCD Monitor
Device
TOP247Y
Power Output
45 W
Input Voltage
90-265 VAC
Output Voltage
12 V
®
Topology
Flyback
Design Highlights
• High efficiency, >82% at 90 VAC
• Low part count solution
• Extremely low EMI – frequency jitter helps meet EN55022B
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
• Differential and common mode surge immunity to
4 kV (EN61000-4-5)
• 100 kHz ring wave immunity to 4 kV (IEEE C62.41)
current limit is further reduced as a function of line voltage
by R4-R6 to provide approximately constant overload power
vs. line. The larger
TOPSwitch-GX
selection reduces
conduction losses, raising efficiency (without circuit changes
or increased overload power), and permits a high inductance
design with a small EE30 core for higher efficiency.
Key Design Points
• Nominal UV and OV set points are calculated according
to the equations:
V
UV
= (50
µA
x
R1) + 2.5 V, V
OV
= (R1
x
225
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).
• T1 shield winding (pins 2-3) reduces EMI. R7 damps
ringing caused by shield capacitive currents.
Operation
The design in Figure 1 utilizes the TOP247Y and takes advantage
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,
removing the need for an input MOV. Resistor R8 programs the
internal current limit of the TOP247Y to 50% of nominal. The
R4-R6
2.7 MΩ
R18
68
Ω
0.5 W
VR1
P6KE
200
CY1
R7 2.2 nF
220
Ω
Y1
L3
Bead
L4
Bead
7, 9
Note: Beads L3 and L4
are placed on D7
anode leads
L2
3.3
µH,
5 A
L6
1T Through
Ferrite Bead
12 V, 3.75 A
C10
100 nF
D1
D1-D4
RL205
2 A, 600 V
F1
L
3.15 A
90-265
VAC
N
CX1
330 nF
X2
t°
RT1
5
Ω,
2.8 A
GND
L1
10 mH
1.4 A
D2
R4
T1
2
3
D7
MBR20100
C1
100
µF
400 V
C2
20 nF
1 kV
R5
C3
4.7 nF
1 kV
D5
UF4005
R6
D
C7, C8
680
µF
35 V
C9
220
µF
35 V
10,12
5
U2
LTV817A
R11
1 kΩ
R13
38.3 kΩ
1%
RTN
R1
2 MΩ
0.5 W
1
D6
1N4148
D3
D4
S
4
6
L
TOPSwitch-GX
U1
CONTROL
CONTROL
C
TOP247Y
R9
6.8
Ω
C5
47
µF
10 V
C6
1
µF
50 V
R10
470
Ω
X
F
L5
3T Ground Wire
Through Ferrite Bead
R8
15 kΩ
C4
100 nF
C11
47 nF
R12
4.7 kΩ
U3
TL431
R14
10 kΩ
1%
C12
22
µF
25 V
PI-3003-051303
Figure 1. TOPSwitch-GX 45 W LCD Monitor Adapter.
DI-21
www.powerint.com
May 2003
POWERINT [ POWER INTEGRATIONS, INC. ]
