TOP250F-TL datasheet(23/52 Pages) POWERINT

23 / 52 page

TOP242-250

12/04

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 heatsink 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

fromlinesurgesandtransientsbysensingwhen

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. Diode D10

for the 5 V output is a PN type to center the 5 V output at 5 V.

The 3.3 V and 5 V output require two capacitors in parallel to

meet the ripple current requirement. Switching noise ﬁltering

is provided by L2 to L5 and C8, C10, C12, C15 and C18.

Resistor R6 prevents peak charging of the lightly loaded 30 V

output. The outputs are regulated using a secondary reference

(U3). Both the 3.3 V and 5 V outputs are sensed via R11

and R10. Resistor R8 provides bias for U3 and R7 sets the

overall DC gain. Resistor R9, C19, R3 and C5 provide loop

compensation. A soft-ﬁnish capacitor (C20) eliminates output

overshoot.

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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