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Design Idea DI-41

Multi-output Set-top Box Power Supply

September 2002

DI-41

®

Application

Set-top Box

TOP247Y

3.3 V, 5 V, 12 V, 18 V, 33 V

Power Output

43 W cont. / 57 W pk

Input Voltage

Output Voltage

Topology

Device

90-132 VAC

Flyback

Design Highlights

• Low cost, low component count solution

• Excellent output voltage tracking and cross-regulation - no

linear regulators required

• High efficiency, >71% at 90 VAC

• Line undervoltage detection (UV) and power system surge

protection (OV)

•Meets CISPR22B/EN55022B conducted EMI limits

• Differential and common mode surge immunity to 4 kV

(EN61000-4-5)

• 100 kHz ring wave immunity to 4 kV (IEEE C62.41)

Figure 1. TOPSwitch-GX 43 W Continuous, 57 W Peak Set-Top Box Power Supply.

®

Operation

The design in Figure 1 utilizes the TOP247Y and takes

advantage of many of the TOPSwitch-GX features. Line UV

and OV (100 V and 450 V, respectively) are implemented

using a single 2 M

Ω resistor (R1). Undervoltage eliminates

output glitches and overvoltage provides protection for both

short duration transients and long duration power system

surges. Resistor R4 programs the internal current limit of U1

to 80% of nominal, limiting overload power.

The key performance characteristic of the circuit shown is the

excellent output voltage tracking and cross-regulation. Two

techniques are used to properly center the output voltages.

The extra voltage drop of the ultra-fast rectifier D10 (used

instead of a Schottky) centers the 5 V output at precisely 5 V

D6

1N4148

D7

UF4003

D8

UF5402

D9

UF5402

D11

MBR1045

D10

BYV32-200

U3

TL431CLP

C20

22

µF

50 V

R7

150

Ω

R11

10 k

Ω

1%

C19

0.1

µF

50 V

R10

9.53 k

Ω

1%

R8

1 k

Ω

C6

2.2 nF

Y1

C7

47

µF

50 V

C9

1000

µF

25 V

C11

390

µF

35 V

C13, C14

1200

µF

35 V

33 V, 0.03 A

18 V, 0.5 A

12 V,

0.6 A/1.8 A pk

5 V, 3.2 A

3.3 V, 3 A

RTN

D1-D4

RL206

2 A, 800 V

F1

3.15 A

RV1

275 V

14 mm

L1

20 mH

1.3 A

t

°

L

N

R3

6.8

Ω

C5

47

µF

16 V

U1

TOP247Y

DL

S

C

TOPSwitch-GX

R1

2 M

Ω

1/2 W

R2

68 k

Ω

2 W

R6

10

Ω

RT1

10

Ω

3.2 A

C2

150

µF

200 V

C5

1 nF

1 kV

C3

1

µF

50 V

C1

0.22

µF

X2

PI-3389-091702

CONTROL

CONTROL

R13

15 k

Ω

1%

C3

0.1

µF

50 V

XF

D5

1N4937

C16, 17

1200

µF

35 V

C15

220

µF

16 V

C18

220

µF

16 V

C12

100

µF

25 V

R14

5.6 k

Ω

0.5 W

C10

220

µF

25 V

C8

10

µF

50 V

L6

33

µH, 0.2 A

L3

3.3

µH, 5 A

L4

3.3

µH

5A

L5

3.3

µH

5A

R4

9.09 k

1%

90 - 132

VAC

D2

D1

D4

D3

VR1

P6KE200

T1

14

13

12

8

9

11

10

3, 4

C22

0.1

µF

50 V

L2

3.3

µH, 5 A

L7

Bead

R15

10

Ω

C24

0.1

µF

50 V

R9

3.3 k

Ω

C21

0.1

µF

50 V

1

5

7

6

R12

18 k

Ω

U2

LTV817