TOP242 Power Integrations Inc., TOP242 Datasheet - Page 24

• Manufacturer Part Number: TOP242
• Description: Family Extended Power/ Design Flexible/Integrated Off-line Switcher
• Manufacturer: Power Integrations Inc.

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 cont./60 W peak (thermally limited) from an input voltage
of 185 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.
Figure 44. 60 W Multiple Output Power Supply using TOP246.
24
TOP242-249
0.1 µF
PERFORMANCE SUMMARY
Output Power:
Regulation:
3.3 V:
5 V:
12 V:
18 V:
30 V:
Efficiency:
No Load Consumption:
J1
C1
X1
L
N
20 mH
0.8A
E
7/01
L1
3.15 A
14 mm
275 V
RV1
1N4007 V
F1
D1-D4
1.7 A
10 Ω
RT1
August 8, 2000
TOP246Y
68 µF
400 V
C2
P6KE170
U1
45 W Cont./60 W Peak
± 5%
± 5%
± 7%
± 7%
± 8%
≥75%
0.6 W
VR1
D
S
D6
1N4937
68 kΩ
CONTROL
CONTROL
2 W
R5
X
L
2 MΩ
1/2 W
TOPSwitch-GX
F
R1
2.2 nF
400 V
1 nF
C
C6
Y1
C5
9.08 kΩ
0.1 µF
50 V
C3
.R2
T1
47 µF
6.8 Ω
10 V
R3
C5
1N4148
10 Ω
R6
D6
D10
BYV32-200
D8
UF5402
D9
UF5402
D11
MBR1045
D7
UF4003
47 µF
50 V
C7
1 µF
50 V
330 µF
C3
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 C4 provide loop
compensation. A soft-finish capacitor (C20) eliminates output
overshoot.
25 V
C9
390 µF
35 V
C11
1000 µF
C13
25 V
22 µF
10 V
C20
1000 µF
1000 µF
C14
25 V
C17
25 V
1000 µF
C16
25 V
LTV817
150 Ω
R7
U2
3.3 µH
3.3 µH
3.3 µH
3.3 µH
U3
TL431
L2
L3
L4
L5
3A
3A
5A
5A
3.3 kΩ
220 µF
1 kΩ
R9
C18
16 V
R8
220 µF
165 V
C15
0.1 µF
C19
9.53
10 k
R11
R12
kΩ
100 µF
C12
25 V
15.0
100 µF
R10
kΩ
C10
25 V
10 µF
50 V
C8
PI-2693-033001
30 V @
18 V @
12 V @
5 V @
3.3 V @
0.03 A
0.5 A
0.6 A
3.2 A
3 A
RTN