www.powerint.com

Design Idea DI-66

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

F

X

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

1

T1

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