TOP242-249
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
45Wcont./60Wpeak(thermallylimited)fromaninputvoltage
of 185 to 265 VAC. Efficiency at 45 W, 185 VAC is ≥ 75%.
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.
The3.3Vand5Voutputsareregulatedto 5%withouttheneed
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.
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 C4 provide loop
compensation. A soft-finish capacitor (C20) eliminates output
overshoot.
Due to the high ambient operating temperature requirement
typical of a set-top box (60 °C) the TOP246Y is used to reduce
conductionlossesandminimizeheatsinksize. ResistorR2sets
the device current limit to 80% of typical to limit overload
power. Thelinesenseresistor(R1)protectstheTOPSwitch-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
powerquality. Athermistor(RT1)isusedtopreventpremature
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.
PERFORMANCE SUMMARY
Output Power:
Regulation:
3.3 V:
5 V:
12 V:
18 V:
30 V:
45 W Cont./60 W Peak
R6
10 Ω
D7
5%
5%
7%
7%
8%
≥75%
0.6 W
30 V @
0.03 A
UF4003
L2
C7
C8
3.3 µH
D8
UF5402
47 µF
10 µF
3A
18 V @
0.5 A
50 V
50 V
C9
L3
C10
Efficiency:
No Load Consumption:
D9
UF5402
330 µF
3.3 µH
100 µF
25 V
12 V @
0.6 A
3A
25 V
C11
C16
C13
C12
C6
2.2 nF
Y1
L4
390 µF
1000 µF
1000 µF
100 µF
3.3 µH
35 V
25 V
25 V
25 V
5 V @
3.2 A
5A
VR1
P6KE170
R5
68 kΩ
C14
C15
L5
2 W
1000 µF
220 µF
D10
3.3 µH
25 V
165 V
3.3 V @
3 A
BYV32-200
5A
C5
1 nF
400 V
C18
D11
MBR1045
C17
220 µF
1000 µF
16 V
D1-D4
1N4007 V
25 V
RTN
D6
1N4937
C2
L1
20 mH
0.8A
68 µF
R10
400 V
D6
1N4148
C3
R7
15.0
1 µF
150 Ω
R1
kΩ
50 V
2 MΩ
C1
0.1 µF
X1
U2
LTV817
T1
R8
1 kΩ
1/2 W
R11
9.53
kΩ
TOPSwitch-GX
D
S
L
RV1
275 V
14 mm
C19
0.1 µF
CONTROL
R9
3.3 kΩ
C
F1
3.15 A
C3
TOP246Y
U1
R3
6.8 Ω
0.1 µF
X
F
J1
50 V
RT1
U3
TL431
C5
C20
22 µF
10 V
10 Ω
.R2
9.08 kΩ
L
R12
10 k
47 µF
1.7 A
10 V
N
PI-2693-033001
Figure 44. 60 W Multiple Output Power Supply using TOP246.
E
7/01
August 8, 2000
24
POWERINT [ Power Integrations ]
