Design Idea DI-66
®
TOPSwitch-GX
45 W, Universal Input,
LCD Monitor Internal Supply
Application
LCD Monitor
Device
TOP246Y/F
Power Output
45 W
Input Voltage
90-265 VAC
Output Voltage
5 V / 12 V
Topology
Flyback
Design Highlights
• 66 kHz operation enables 0.45 W of standby output
power delivery with 0.9 W of input power at 230 VAC
• Low no-load input power: <0.42 W at 230 VAC
• 82% efficient (min) at 90 VAC input and 45 W output
• Low component count: only 52 parts!
• Meets CISPR22 B EMI with
>
10 dB of margin
• No TVS required for the primary snubber
Operation
Many of the built-in features of
TOPSwitch-GX,
such as line
UV/OV, soft start, line feed-forward, accurate current limit,
and frequency jitter have been used to reduce the component
count, transformer size and overall system cost of this universal
input, flyback power supply. This design is ideal for LCD
monitor supplies that require low standby power consumption.
The switching frequency of U1 is set to 66 kHz by connecting
its F pin to the CONTROL pin. Efficient 66 kHz operation
results from the use of an EER3016S core to keep the number
of primary turns low and to further reduce T1 leakage inductance.
This reduces the losses due to both leakage inductance and
winding capacitance. Low leakage inductance also allows the
use of a low cost RCD snubber (C3, R2–R4 and D5) to clamp
the U1 DRAIN voltage, while keeping standby power
consumption low. Use of a glass-passivated normal recovery
diode (D5) recycles the stored leakage energy and increases the
overall efficiency. Resistor R4 dampens drain node ringing,
and is necessary when a normal recovery diode is used.
Resistor R5 sets nominal UV and OV limits to 84 V and 378 V,
respectively. Under-voltage lockout protects the supply from
overheating during brownout, and eliminates power-up and
power-down glitches. Overvoltage shutdown protects the power
supply from line surges.
R2
68 k
1/2 W
R3
68 k
1/2 W
D1-D4
RL205
CY1
330 pF
Y1 CX1
330 nF
X2
CY2
330 pF
Y1
F1
3.15 A
250 V
RT1
5/3 A
L1
5.3 mH
1A
C1
100
µF
400 V
C3
10n
1 kV
R4
10
1/2 W
R5
2M
Ω
1/2 W
D5
1N4007G
1
T1
CY3
2.2 nF
R12
C8
68
Ω
470 pF
L2
3.3 uH
C9
680
µF
16 V
12 V/ 3 A
NEUT
R2
2M
1/2 W
5
10
D12
MBR20100CT
C10
680
µF
16 V
L3
3.3 uH
C15
330 nF
C11
100
µF
25 V
5 V/1.8 A
2
6,7
D13
SB540
C12
680
µF
10 V
C13
680
µF
10 V
8,9
3
C6
47
µF
50 V
U2
PC817C
GND
R6
7.5M
1/2 W
R13
390
Ω
R14
22
Ω
C14
100
µF
25 V
RTN
90-265
VAC
TOPSwitch-GX
U1
TOP246Y
D
L
CONTROL
C
LINE
4
D10
LL4148
R15
1.0 kΩ
R16
10.0 kΩ
S
X
F
R8
6.8
Ω
C4
100 nF
C5
47µF
10 V
R9
330
Ω
C17
10
µF
35 V
C16
47 nF
R17
2.2 kΩ
U3
LM431AIM3
R7
7.87 kΩ
L4
6 x 5 mm
Bead Ferrite
R18
10.0 kΩ
PI-3743-120904
Figure 1. Circuit Diagram of a TOP246 Based LCD Monitor Power Supply.
DI-66
www.powerint.com
December 2004
POWERINT [ POWER INTEGRATIONS, INC. ]
