www.powerint.com

Design Idea DI-21

Input, LCD Monitor External Adapter

May 2003

DI-21

®

Application

LCD Monitor

TOP247Y

12 V

Power Output

45 W

Input Voltage

Output Voltage

Topology

Device

90-265 VAC

Flyback

Figure 1. TOPSwitch-GX 45 W LCD Monitor Adapter.

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)

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 M

Ω

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

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

• 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.

®

U2

LTV817A

L3

Bead

L4

Bead

U1

TOP247Y

DL

SX

F

C

D1-D4

RL205

2 A, 600 V

D3

D4

D1

D2

GND

90-265

VAC

F1

3.15 A

CX1

330 nF

X2

RT1

5 Ω, 2.8 A

L5

3T Ground Wire

Through Ferrite Bead

L6

1T Through

Ferrite Bead

Note: Beads L3 and L4

are placed on D7

anode leads

C1

100 µF

400 V

C2

20 nF

1 kV

R4-R6

2.7 MΩ

R18

68 Ω

0.5 W

R8

15 kΩ

C6

1 µF

50 V

CY1

2.2 nF

Y1

C3

4.7 nF

1 kV

D5

UF4005

D6

1N4148

C7, C8

680 µF

35 V

C9

220 µF

35 V

C10

100 nF

RTN

12 V, 3.75 A

R7

220 Ω

VR1

P6KE

200

2

PI-3003-051303

TOPSwitch-GX

7, 9

6

5

L

N

C4

100 nF

C5

47 µF

10 V

R9

6.8 Ω

U3

TL431

R14

10 kΩ

1%

R11

1 kΩ

C11

47 nF

C12

22 µF

25 V

L2

3.3 µH, 5 A

D7

MBR20100

R4

R5

R6

t°

CONTROL

CONTROL

10,12

T1

R13

38.3 kΩ

1%

R12

4.7 kΩ

L1

10 mH

1.4 A

R1

2 MΩ

0.5 W

4

3

1

R10

470 Ω