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Design Idea DI-16

Multi-output Set-top Box Power Supply

December 2002

DI-16

®

Application

Set-top Box

TOP246Y

3.3 V / 5 V / 12 V / 18 V / 33 V

Power Output

43 W cont./57 W peak

Input Voltage

Output Voltage

Topology

Device

180-265 VAC

Flyback

Design Highlights

• High efficiency, >75% at 180 VAC

• Good cross-regulation with no linear regulators

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

power system surge protection

•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)

Key Design Points

•R1 (2 M

Ω, 0.5 W) sets UV at 100 VDC and OV at

450 VDC. A 0.5 W resistor is required to give a voltage

rating greater than 350 VDC.

• Integrated OV shut-down protects against long duration line

voltage surges (common in some countries). During shut-

down, the drain voltage does not exceed the DC input

voltage (drain does not switch), allowing the AC rail to

rise to 495 VAC (700 VDC BV

without

damaging the TOPSwitch-GX.

• Transformer T1 is constructed using a slotted bobbin,

enabling automated transformer winding and assembly.

• The transformer turns ratio is optimized (including output

diode forward drops) to minimize the output voltage error

between the 3.3 V and 5 V outputs.

• Feedback is taken from both the 3.3 V and 5 V outputs to

the reference (U3) via R10, R11 and R13. Other output

voltages are set by the transformer turns ratio. The 12 V,

18 V, and 33 V outputs are DC-stacked on the 5 V output

for enhanced regulation and voltage centering. Pre-load

resistor R14 is required to maintain regulation of the 33 V

output when lightly loaded.

Figure 1. TOPSwitch-GX 60 W Set-top Box Output Power Supply.

®

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 kΩ

1%

C19

0.1 µF

50 V

R10

9.53 kΩ

1%

R8

1 kΩ

C6

2.2 nF

Y1

C7

47 µF

50 V

C9

1000 µF

25 V

C11

390 µF

35 V

C13, C14

1000 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

1N4007V

1 A, 1000 V

F1

3.15 A

RV1

275 V

14 mm

L1

20 mH

0.8 A

t°

L

N

R3

6.8 Ω

C5

47 µF

16 V

U1

TOP246Y

DL

S

C

TOPSwitch-GX

R1

2 MΩ

1/2 W

R2

68 kΩ

2 W

R6

10 Ω

RT1

10 Ω

1.7 A

C2

68 µF

400 V

C5

1 nF

1 kV

C3

1 µF

50 V

C1

0.1 µF

X2

PI-3395-100102

CONTROL

CONTROL

R13

15 kΩ

1%

C3

0.1 µF

50 V

XF

D5

UF4005

C16, 17

1000 µF

35 V

C15

220 µF

16 V

C18

220 µF

16 V

C12

100 µF

25 V

R14

2.7 kΩ

0.5 W

C10

100 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%

180 - 265

VAC

D2

D1

D4

D3

VR1

P6KE200

T1

18

17

16

10

14, 15

11

3, 4

L2

3.3 µH, 5 A

L7

Bead

R15

C24

0.1 µF

50 V

R9

3.3 kΩ

1

5

8

9

U2

LTV817

12, 13

PERFORMANCE SUMMARY

Output Power:

45 W Cont./

57 W Peak

Regulation:

3.3 V:

± 5%

5 V:

± 5%

12 V:

± 7%

18 V:

± 7%

33 V:

± 8%

Efficiency:

≥75%

No-Load Consumption:

0.6 W