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Design Idea DI-66
TOPSwitch-GX
45 W, Universal Input,
LCD Monitor Internal Supply
December 2004
DI-66
®
Application
LCD Monitor TOP246Y/F 5 V / 12 V
Power Output
45 W
Input Voltage Output Voltage Topology
Device
90-265 VAC Flyback
Figure 1. Circuit Diagram of a TOP246 Based LCD Monitor Power Supply.
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.
D
S
C
L
FX
CONTROL
PI-3743-120904
12 V/ 3 A
5 V/1.8 A
RTN
U1
TOP246Y
U2
PC817C
U3
LM431AIM3
90-265
VAC
NEUT
GND
LINE
C5
47µF
10 V
C4
100 nF
R7
7.87 kΩ
L4
6 x 5 mm
Bead Ferrite
5
2
1T1
6,7
8,9
3
4
10
R18
10.0 kΩ
R16
10.0 kΩ
R9
330 Ω
R8
6.8 Ω
R6
7.5M
1/2 W
R2
2M
1/2 W
RT1
5/3 A
F1
3.15 A
250 V
R17
2.2 kΩ
R15
1.0 kΩ
C17
10 µF
35 V
C16
47 nF
C14
100 µF
25 V
C11
100 µF
25 V
C10
680 µF
16 V
C9
680 µF
16 V
C12
680 µF
10 V
C13
680 µF
10 V
D13
SB540
D5
1N4007G
D12
MBR20100CT
C6
47 µF
50 V
D10
LL4148
C15
330 nF
L3
3.3 uH
L2
3.3 uH
R14
22 Ω
R13
390 Ω
R4
10
1/2 W
R5
2M Ω
1/2 W
R3
68 k
1/2 W
D1-D4
RL205
C3
10n
1 kV
C1
100 µF
400 V
CY1
330 pF
Y1
CY2
330 pF
Y1
CX1
330 nF
X2
R12
68 Ω
CY3
2.2 nF
C8
470 pF
L1
5.3 mH
1 A
R2
68 k
1/2 W
TOPSwitch-GX
Power Integrations 5245 Hellyer Avenue San Jose, California 95138
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The PI logo,
TOPSwitch
,
TinySwitch
,
LinkSwitch
,
DPA-Switch
and
EcoSmart
are registered trademarks of Power Integrations.
PI Expert
and
PI FACTS
are trademarks of Power Integrations. Copyright 2004, Power Integrations
Power Integrations may make changes to its products at any time. Power Integrations has no liability arising from your use of any information, device or circuit described
herein nor does it convey any license under its patent rights or the rights of others. POWER INTEGRATIONS MAKES NO WARRANTIES HEREIN AND SPECIFICALLY
DISCLAIMS ALL WARRANTIES INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE,
AND NON-INFRINGEMENT OF THIRD PARTY RIGHTS. The products and applications illustrated herein (including circuits external to the products and transformer
construction) 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
.
For the latest updates, visit
www.powerint.com
www.powerint.com
B
12/04
DI-66
Table 1. Transformer Construction Information.
Core
Bobbin
Winding Details
Winding Order
(pin numbers)
Primary Inductance
Primary Resonant
Frequency
Leakage Inductance
TRANSFORMER PARAMETERS
Samwha EER3016S-PL-7
ALG of 342 nH/T2
10 Pin, EER3016S
1/2 Primary: 28 T, 26 AWG
Bias: 7T, 2 x 26 AWG
12 V Secondary, 4T, 2 x 25 AWG
Triple Insulated Wire
5 V Secondary: 3T, 3 x 25 AWG
Triple Insulated Wire
1/2 Primary: 24T, 26 AWG
1/2 Primary: 2-5, tape 1L
Bias: 3-4, tape 2L
12 V Secondary: 10-6,7
5 V Secondary: 6,7-8,9, tape 2L
1/2 Primary: 5-1, tape 3L
919 µH ±10%
1.1 MHz (Min)
18 µH (Max)
0 0.2 0.30.1 0.4 0.5 0.6 0.7
Output Power (W)
Input Power (W)
0.6
0.7
0.3
0.4
0.5
0.2
1
1.1
0.8
0.9
1.2
PI-3744-102403
230 VAC
115 VAC
-20
-10
0
10
20
30
40
50
60
70
80
0.15 1 10 70
Frequency (MHz)
Amplitude (dBµV)
PI-3745-102403
(QP)
(AV)
Quasi-Peak Scan
Average Scan
Figure 3. Pin vs. Pout, 5 V Output Loaded, No Load
on 12 V Output.
Figure 2. Conducted EMI, CISPR22B Limits, Maximum Load, Secondary
Return Connected to Safety Ground, 230 VAC Input.
Effective EMI filtering is accomplished with only five parts
(L1, CX1, CY1-CY3), due to the built-in frequency jitter
function of TOPSwitch-GX.
Key Design Points
•Use 66 kHz operation to reduce standby power loss.
•To reduce the number of primary turns required for
66 kHz operation, the Ae of the T1 core must be large.
Recommended cores are EER3016S and PQ2620.
•Split-primary transformer construction should be used to
keep leakage inductance to a minimum.
•Use an RCD snubber with the normal recovery diode. Size
resistors R2 and R3 for the highest value that ensures
adequate drain voltage margin under overload conditions at
high line.
