TOP232P datasheet(15/36 Pages) POWERINT

15 / 36 page

TOP232-234

7/01

Figure 25. 35 W Set-Top Box Power Supply.

35 W Multiple Output Power Supply

Figure 25 shows a five output, 35 W, secondary regulated

power supply utilizing a TOP233 for multiple output applications

such as set-top box, VCR, DVD, etc. The circuit shown is

designed for a 230 VAC input but can be used over the universal

range at a derated output power of 25 W. Alternatively, a

doubler input stage can be used at 100 or 115 VAC for the full

power rating of 35 W. TOPSwitch-FX provides several

advantages in the above mentioned applications.

A single line sense resistor R1 (2 M

Ω) implements an under-

voltage detect (at 100 V), over-voltage shutdown (at 450 V) and

line feed forward with DC

MAX reduction features.

Under-

voltage detect ensures that the outputs are glitch free on power

down. The over-voltage shutdown turns off the TOPSwitch-FX

MOSFET above 450 V on the DC input rail, eliminating

reflected voltage and leakage inductance spikes, and hence,

extending the surge withstand to the 700 VDC rating of the

MOSFET. This feature prevents field failures in countries

where prolonged line voltage surges are common.

This design also takes advantage of soft-start and higher operating

frequency to reduce transformer size. A snubber circuit (R4,

C4) is used to slowdown dv/dt of the switching waveform

minimizing radiated video noise that could interfere with TV

reception. The half frequency option of the TOPSwitch-FX can

be used by connecting the FREQUENCY pin to the CONTROL

pin instead of the SOURCE pin in video noise sensitive

applications to allow for heavier snubbing without significant

impact on efficiency.

This design achieves

±5% load regulation on 3.3 V and 5 V

outputs using dual sensed optocoupler feedback through resistors

R9, R10 and R11. Other output voltages are set by the transformer

turns ratio. Output voltage on the low power -5 V output is shunt

regulated by resistor R12 and Zener diode VR2. Dummy load

resistor R13 is required to maintain regulation of the 30 V

output under light load conditions. Compensation of the TL431

(U3) is achieved with resistor R8 and capacitor C7. Primary

side compensation and auto-restart frequency are determined

by resistor R5 and capacitor C5. Second stage LC post-filtering

is used on the 3.3 V, 5 V and 18 V high power outputs (L2, L3,

L4 and C13, C15, C17) for low ripple. Full load operating

efficiency exceeds 75% across the AC input range. Primary

clamp components VR1 and D1 limit peak drain voltage to a

safe value.

The frequency jittering in TOPSwitch-FX helps reduce EMI,

maintaining emissions below CISPR 22 (FCC B) levels through

proper choice of Y1 capacitor (CY1) and input filtering elements

(CX1, L1). To minimize coupling of common mode transients

to the TOP233, Y1 capacitor is tied to the positive input DC rail.

Lightning strike immunity to 3 kV is attained with the addition

of a 275 V MOV (RV1).

5 V

@ 2.5 A

3.3 V

@ 3 A

RTN

1N4148

LTV817

TL431CLP

µF

Ω

R11

10.0 k

Ω

0.1

µF

9.53 k

Ω

R10

15.0 k

Ω

510

Ω

MUR120

UF5402

C12

220

µF

25 V

CY1

2.2 nF

30 V

@ 100 mA

18 V

@ 550 mA

UF4007

VR1

P6KE200

BR1

400 V

3.15 A

RV1

275 V

20 mH

6.8

Ω

µF

47 pF

TOP233Y

TOPSwitch-FX

2 M

Ω

1/2 W

R13

24 k

Ω

2 k

Ω

µF

400 V

100 nF

C10

100

µF

50 V

D10

MBR1045

C14

1000

µF

25 V

3.3

µH

3.3

µH

C15

100

µF

10 V

C13

100

µF

25 V

C11

µF

50 V

3.3

µH

D11

BYW29-

100

C16

1000

µF

25 V

C18

330

µF

10 V

R12

Ω

D12

1N5819

-5 V

@ 100 mA

CX1

0.1

µF

250 VAC

C17

100

µF

10 V

C19

100

µF

10 V

VR2

1N5231

PI-2536-040401

CONTROL

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