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Design Idea DI-22

External Laptop Adapter

September 2002

DI-22

Figure 1. TOPSwitch-GX 70 W Laptop Adapter Schematic.

Application

Laptop Adapter

TOP249Y

19 V

Power Output

70 W

Input Voltage

Output Voltage

Topology

Device

85-265 VAC

Flyback

®

Design Highlights

• High efficiency: 84% at 85 VAC (with 50 ˚C external

ambient temperature)

• Very compact design (4.1 in.

× 2.225 in. × 1.06 in.)

• No surface mount components required

• Low zero load power consumption, <370 mW at 115 VAC

• Approximately constant overload power with line voltage

• Line undervoltage detection (UV) and overvoltage (OV)

shutdown

• Low EMI - switching frequency jitter helps meet CISPR22B/

EN55022B limits

• Fully protected for overload, short circuit and thermal faults

Operation

The design utilizes a TOP249Y in a flyback converter

providing a 70 W output in a sealed enclosure at an external

ambient of 50 ˚C. 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 glitches and

overvoltage provides line transient and long duration power

system surge protection. Resistor R10 programs the internal

current limit to 75% of nominal at the UV threshold. As a

function of input voltage the current limit is further reduced

by R9 to provide approximately constant overload power.

The larger TOPSwitch-GX selection reduces conduction

losses, raising efficiency (without circuit changes or increased

overload power) and permits a higher inductance design for

reduced primary RMS currents, further increasing efficiency.

PI-2691-033001

®

19 V, 3.6 A

TOP249Y

U1

U3

TL431

U2

PC817A

DL

SX

F

C

RTN

L2

820

µH

2 A

C6

0.1

µF

X2

F1

3.15 A

85-265 VAC

BR1

RS805

8 A 600 V

L3

75

µH

2 A

t

°

T1

C13

0.33

µF

400 V

C12

0.022

µF

400 V

C11

0.01

µF

400 V

RT1

10

Ω

1.7 A

CONTROL

CONTROL

TOPSwitch-GX

C1

150

µF

400 V

C5

47

µF

16 V

C3

820

µF

25 V

L1

200

µH

C2

820

µF

25 V

C14

0.1

µF

50 V

C4

820

µF

25 V

C10

0.1

µF

50 V

C9

4.7 nF 50 V

C8

0.1

µF

50 V

VR1

P6KE-

200

D2

MBR20100

C7 2.2 nF

Y1 Safety

D3

MBR20100

D4

1N4148

R11

2 M

Ω

1/2 W

R9

13 M

Ω

R8

4.7

Ω

R1

270

Ω

R2

1 k

Ω

R13

562

Ω

1%

R4

31.6 k

Ω

1%

R7

56 k

Ω

R10

20.5 k

Ω

R3

6.8

Ω

R6

4.75 k

Ω

1%

C15

1

µF

50 V

D1

UF4006

1

2

3

2

9

6

5

11

8