TOP242 datasheet(23/54 Pages) POWERINT

23 / 54 page

Rev. R 10/20

TOP242-250

www.power.com

and thus ensuring that the output voltage reaches

regulation at start-up under low line, full load conditions.

Resistor R9 provides a discharge path for C14. Capacitor

C13 and R8 provide control loop compensation and are

required due to the gain associated with such a high output

voltage.

Sufficient heat sinking is required to keep the TOPSwitch-GX

device below 110

°C when operating under full load, low

line and maximum ambient temperature. Airflow may also

be required if a large heat sink area is not acceptable.

Multiple Output, 60 W, 185-265 VAC Input

Power Supply

Figure 44 shows a multiple output supply typical for high

end set-top boxes or cable decoders containing high

capacity hard disks for recording. The supply delivers an

output power of 45 W continuous/60 W peak (thermally

limited) from an input voltage of 185 VAC to 265 VAC.

Efficiency at 45 W, 185 VAC is ≥ 75%.

The 3.3 V and 5 V outputs are regulated to ±5% without

the need for secondary linear regulators. DC stacking (the

secondary winding reference for the other output voltages

is connected to the cathode of D10 rather than the anode)

is used to minimize the voltage error for the higher voltage

outputs.

Due to the high ambient operating temperature requirement

typical of a set-top box (60

°C), the TOP246Y is used to

reduce conduction losses and minimize heat sink size.

Resistor R2 sets the device current limit to 80% of typical

to limit overload power. The line sense resistor (R1)

protects the TOPSwitch-GX from line surges and transients

by sensing when the DC rail voltage rises to above 450

V. In this condition the TOPSwitch-GX stops switching,

extending the input voltage withstand to 496 VAC, which

is ideal for countries with poor power quality. A thermistor

(RT1) is used to prevent premature failure of the fuse by

limiting the inrush current (due to the relatively large size of

C2). An optional MOV (RV1) extends the differential surge

protection to 6 kV from 4 kV.

Leakage inductance clamping is provided by VR1, R5

and C5, keeping the DRAIN voltage below 700 V under

all conditions. Resistor R5 and capacitor C5 are selected

such that VR1 dissipates very little power except during

overload conditions. The frequency jittering feature of

TOPSwitch-GX allows the circuit shown to meet CISPR22B

with simple EMI filtering (C1, L1 and C6) and the output

grounded.

The secondaries are rectified and smoothed by D7 to D11,

C7, C9, C11, C13, C14, C16 and C17. Diode D11 for the

3.3 V output is a Schottky diode to maximize efficiency.

Figure 44. 60 W Multiple Output Power Supply using TOP246.

1N4148

UF4003

UF5402

D11

MBR1045

D10

BYV32-200

LTV817

TL431

C20

µF

10 V

150

Ω

R12

10 k

C19

0.1

µF

R11

9.53

Ω

R10

15.0

Ω

3.3 k

Ω

1 k

Ω

2.2 nF

µF

50 V

330

µF

25 V

C11

390

µF

35 V

C14

1000

µF

25 V

30 V @

0.03 A

18 V @

0.5 A

12 V @

0.6 A

5 V @

3.2 A

3.3 V @

3 A

RTN

D1-D4

1N4007 V

3.15 A

RV1

275 V

14 mm

20 mH

0.8A

6.8

Ω

µF

10 V

TOP246Y

TOPSwitch-GX

2 M

Ω

1/2 W

68 k

Ω

2 W

Ω

RT1

Ω

1.7 A

µF

400 V

1 nF

400 V

µF

50 V

0.1

µF

PI-2693-081704

CONTROL

0.1

µF

50 V

1N4937

VR1

P6KE170

C16

1000

µF

25 V

C13

1000

µF

25 V

C17

1000

µF

25 V

C15

220

µF

16 V

C18

220

µF

16 V

C12

100

µF

25 V

C10

100

µF

25 V

µF

50 V

3.3

µH

3.3

µH

3.3

µH

3.3

µH

PERFORMANCE SUMMARY

Output Power:

45 W Cont./60 W Peak

Regulation:

3.3 V:

± 5%

5 V:

± 5%

12 V:

± 7%

18 V:

± 7%

30 V:

± 8%

Efficiency:

≥75%

No Load Consumption:

0.6 W

9.08 k

Ω

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