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Design Idea DI-33

Supply: <50 mW No-load Consumption

September 2002

DI-33

®

Application

DVD Player

TNY268P

+3.3 V, +5.0 V, +12.0 V, -12 V

Power Output

11 W cont. 17 W pk.

Input Voltage

Output Voltage

Topology

Device

85-265 VAC

Flyback

Design Highlights

• No-load input power <50 mW

• 700 mW of output power with 1 W input

• Built-in frequency jitter allows low cost

π filter

• 132 kHz operation minimizes transformer size and turns,

providing good cross-regulation

• High efficiency – >77% minimum

•Meets CISPR22B/EN55022B and FCC B with >10 dB margin

Key Design Points

• An optional low voltage bias circuit, D9 and C10, powers U1

via R6, reducing light and zero load power consumption.

This provides bias current that would otherwise be provided

from the DRAIN by the internal high voltage current source.

The current source is disabled when the BP pin is fed

externally, an internal clamp limiting the voltage to

6.3 V. The bias supply is designed to produce 7.5 V at

no-load. Resistor R6 is chosen to provide

approximately 500

µA into the BP pin, the maximum

consumption at no-load.

• Good cross-regulation on 5 V and 3.3 V outputs is

achieved by minimizing secondary leakage through

Figure 1. TinySwitch-II DVD Player Schematic.

the use of foil windings and dual sense feedback via R15

and R16.

• To minimize potential noise coupling to the SOURCE pin

during common mode surges, the Y1 capacitor C8 is

connected between secondary return and the HV DC rail.

• Resistors R5 and R7 damp ringing to improve EMI.

• Optional soft-finish capacitor C7 eliminates output startup

overshoot.

• Optional under-voltage resistor R1 provides clean startup

and prevents output glitches on power down.

R1 = (V

• Small loop areas in the secondary layout around D10,

C12, D9, C11, D7, C15, D8 and C9 together with post-

filters L2/C20, L3/C17 and L4/C18 provide low output

ripple, below 50 mV p-p.

D

S

BP

PI-3205-091302

EN

U1

TNY268

R5

47

Ω

R7

100

Ω

R1

2 M

Ω

(Optional)

R8

1 k

Ω

R16

6.34 k

Ω

1%

R9

200

Ω

R15

20 k

Ω

1%

R13

10 k

Ω

1%

R10

3.3 k

Ω

R12

1

Ω

1/2 W

D7

UF4003

D9

1N5822

D10

1N5822

D8 UF4003

D6 1N4148

D1 & D2

1N4007

D3 & D4

1N4007

D5

1N4007

F1

L2

3.3 uH

L3

3.3 uH

L4

3.3 uH

U2

PC817

U2

VR1

P6KE180

12 V, 0.4 A

3.3 V, 0.7 A

-12 V, 0.1 A

85-265

VAC

5 V, 1.6 A

RTN

N

L

L1

1.4 mH

0.5 A

C3

0.047

µF

X2

C1 & C4

33

µF

400 V

C8

1 nF

Y1

8

13

9

11

14

6

5,7

1

4

C9

220

µF

25 V

C18

470

µF

10 V

C17

470

µF

10 V

C20

150

µF

25 V

C15

470

µF

25 V

C11

1800

µF

25 V

C12

1000

µF

10 V

C6

220

µF

25 V

C7

10

µF

50 V

U3

TL431

C10

10

µF

50 V

C5

0.1

µF

50 V

C14

0.1

µF

TinySwitch-II

R6

3.3 k

Ω

C2

0.01

µF

1 kV

®