Design Idea DI-41
®
TOPSwitch-GX
43 W, 100/115 VAC
Multi-output Set-top Box Power Supply
Application
Set-top Box
Device
TOP247Y
Power Output
43 W cont. / 57 W pk
Input Voltage
90-132 VAC
Output Voltage
3.3 V, 5 V, 12 V, 18 V, 33 V
®
Topology
Flyback
Design Highlights
• Low cost, low component count solution
• Excellent output voltage tracking and cross-regulation - no
linear regulators required
• High efficiency, >71% at 90 VAC
• Line undervoltage detection (UV) and power system surge
protection (OV)
• Meets CISPR22B/EN55022B conducted EMI limits
• Differential and common mode surge immunity to 4 kV
(EN61000-4-5)
• 100 kHz ring wave immunity to 4 kV (IEEE C62.41)
Operation
The design in Figure 1 utilizes the TOP247Y and takes
advantage of many of the
TOPSwitch-GX
features. Line UV
and OV (100 V and 450 V, respectively) are implemented
using a single 2 MΩ resistor (R1). Undervoltage eliminates
output glitches and overvoltage provides protection for both
short duration transients and long duration power system
surges. Resistor R4 programs the internal current limit of U1
to 80% of nominal, limiting overload power.
The key performance characteristic of the circuit shown is the
excellent output voltage tracking and cross-regulation. Two
techniques are used to properly center the output voltages.
The extra voltage drop of the ultra-fast rectifier D10 (used
instead of a Schottky) centers the 5 V output at precisely 5 V
L6
33
µH,
0.2 A
C7
47
µF
50 V
C9
1000
µF
25 V
L2
3.3
µH,
5 A
L3
3.3
µH,
5 A
C8
10
µF
50 V
C10
220
µF
25 V
33 V, 0.03 A
T1
14
R6
10
Ω
D8
UF5402
D9
UF5402
D7
UF4003
13
18 V, 0.5 A
12 V,
0.6 A/1.8 A pk
12
8
L7
Bead
C24
R15
0.1
µF
10
Ω
50 V
C11
390
µF
35 V
L4
3.3
µH
5A
C13, C14
1200
µF
35 V
C16, 17
1200
µF
35 V
L5
C15
3.3
µH
220
µF
5A
16 V
C18
220
µF
16 V
C12
100
µF
25 V
R14
5.6 kΩ
0.5 W
5 V, 3.2 A
C5
R2
68 kΩ 1 nF
2 W 1 kV
C6
2.2 nF
Y1
1
9
D1-D4
RL206
2 A, 800 V
D2
D1
D5
1N4937
D4
L1
20 mH
1.3 A
C1
0.22
µF
X2
RV1
275 V
14 mm
F1
3.15 A
L
90 - 132
VAC
D10
BYV32-200
11
3.3 V, 3 A
VR1
P6KE200
3, 4
D11
MBR1045
10
C22
0.1
µF
50 V
RTN
D3
C2
150
µF
200 V
R1
2 MΩ
1/2 W
5
7
R7
150
Ω
D6
1N4148
C3
1
µF
50 V
U2
LTV817
R8
1 kΩ
C19
0.1
µF
50 V
R10
9.53 kΩ
1%
C21
0.1
µF
50 V
R12
18 kΩ
R13
15 kΩ
1%
6
D
L
TOPSwitch-GX
C
U1
TOP247Y
RT1
10
Ω
3.2 A
R4
9.09 k
1%
S
CONTROL
X
F
t°
C3
0.1
µF
50 V
R3
6.8
Ω
C5
47
µF
16 V
C20
22
µF
50 V
R9
3.3 kΩ
U3
TL431CLP
R11
10 kΩ
1%
PI-3389-091702
N
Figure 1. TOPSwitch-GX 43 W Continuous, 57 W Peak Set-Top Box Power Supply.
DI-41
www.powerint.com
September 2002
DI-41
and DC stacking is used to improve the regulation of 12 V,
18 V, and 30 V outputs. Ferrite bead L7 is placed in series with
the 12 V, 18 V and 30 V output windings to improve centering
and cross-regulation of these outputs.
Frequency jittering provides large EMI margins with simple
filtering. Primary soft-start minimizes component stress during
start-up and a soft-finish capacitor (C20) eliminates start-up
output overshoot.
TRANSFORMER PARAMETERS
Core Material
ERL28, Nippon ceramic
NC-2H material or equivalent,
gapped for
A
LG
= 128 nH/T
2
ERL28 vertical, 14 pins,
Jinbo Industrial
JB-0039 or equivalent
Primary: 30T + 23T, 25 AWG
Shield: 1T, 0.6" x 0.001" Cu foil
Bias: 7T, 2 x 27 AWG
3.3 V: 2T, 0.6" x 0.005" Cu foil
5 V: 1T, 0.6" x 0.005" Cu foil
12 V: 4T, 2 x 27 AWG
18 V: 3T, 2 x 27 AWG
33 V: 6T, 27 AWG
(2 x 27 AWG = Bifilar 27 AWG)
Apply 3.2 mm tape margin to
both sides of bobbin
Primary (4-3), tape, Shield (1-NC),
tape, Bias (6-7), 3 x tape, 5 V (9-11),
3.3 V (11-10), tape, 12 V (12-8),
18 V (13-12), 33 V (14-13),
3 x tape, Primary (3-1), 3 x tape
Primary: 356
µH,
Leakage: 11
µH
(maximum)
650 kHz (minimum)
Bobbin
Key Design Points
Winding Details
• Use K
RP
(Ripple-to-peak current ratio) in the range of
0.4–0.6 for higher efficiency, and tighter cross-regulation.
Use V
OR
(reflected output voltage) of 90 V to 110 V for
optimum performance.
• PCB traces which carry high switching currents should be
short and wide to reduce EMI.
• Reduce leakage inductance and improve cross-regulation
by filling each winding layer across the entire width of the
bobbin.
• Resistor R14 provides a small amount of pre-load on the
33 V output to prevent peak charging due to leakage
spikes.
• R5 and C5 reduce power dissipation in VR1.
Voltage
Load
Range
(Amp)
-8 -7 -6
1-3
1-3.2
0.3-0.6
0.01-0.03
Winding Order
(Pin Numbers)
Inductance
Primary Resonant
Frequency
Regulation (%)
-5
-4
-3
-2
-1
0
1
2
3
Table 1. Transformer Design Parameters.
(V)
3.3
5
12
30
Table 2. Worst Case Output Cross Regulation - Outputs Taken
from Minimum to Maximum Load and Line from 85 VAC
to 132 VAC.
For the latest updates, visit our Web site:
www.powerint.com
Power Integrations reserves the right to make changes to its products at any time to improve reliability or manufacturability.
Power Integrations does not assume any liability arising from the use of any device or circuit described herein, nor does it convey any
license under its patent rights or the rights of others. The products and applications illustrated herein may be covered by one or more U.S.
and foreign patents or potentially by pending U.S. and foreign patent applications assigned to Power Integrations. A complete list of Power
Integrations’ patents may be found at www.powerint.com.
The PI Logo,
TOPSwitch
,
TinySwitch
and
EcoSmart
are registered trademarks of Power Integrations, Inc.
PI Expert
is a trademark of Power Integrations, Inc. ©Copyright 2002, Power Integrations, Inc.
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