Design Idea DI-55
®
TOPSwitch-GX
Application
DVD
Device
TOP245P
20 W (25 W peak) DVD Supply
Power Output
20 W (25 W pk)
Input Voltage
85-265 VAC
Output Voltage
3.3 V / 5 V / 12 V / -24 V
Topology
Flyback
Design Highlights
• Simple, low cost, low part count solution
• No heatsinks required
• Low EMI-frequency jitter allows EN55022B/FCC B
compliance with simple EMI filter
• High efficiency, >75% at 90 VAC
• Low zero load power consumption, <100 mW at
230 VAC
• Low standby power consumption, <1 W input at 0.5 W
output, 230 VAC
• Excellent cross-regulation
• Differential and common mode surge immunity to 3 kV
(EN 61000-4-5)
The external current limit programming and remote ON/OFF
(inhibit) functions of the M pin allow current mode control
and reduced switching frequency at light and no-load condi-
tions. Current mode control is implemented by R2, Q3, R3,
C16, R4 and R6.
Feedback current above ~2 mA (U1 supply current) forward
biases Q3 and pulls up R6. This adjusts the sink current out
of the M pin, thereby allowing the output voltage feedback
loop to control the primary switch current.
Resistor R6 sets the maximum current limit, while R2 and
C16 provide slope compensation. The value of R4 is chosen
to ensure that current does not flow into the M pin, enabling
the line sensing features of the pin. The current out of the
M pin falls as the load is reduced until the M pin inhibit
threshold is reached. The supply then operates with a fixed
25% current limit, lowering the switching frequency to
maintain regulation. This greatly reduces switching losses,
maintaining high standby efficiency and low no-load power
consumption.
L5
BEAD
D7
1N5819
C15
470
µF
25 V
C20
180
µF
25 V
L3
3.3
µH
D11
SB540CT
C12
1200
µF
10 V
C17
R14
470
µF
1.13 kΩ
10 V
1%
L2
3.3
µH
Operation
The TOP245P selected for the design in Figure 1 is ideal for
DVD and set-top box applications. The P package removes the
need for a heatsink while still delivering 20 W/25 W peak at
an ambient temperature of 50
°C.
C1
33
µF
400 V
VR1
C4
33
µF
P6KE
400 V 130
L1
C8
2.2 nFY1
T1
EE25L
8
+12 V, 500mA
F1
3.15 A
J1-2
250 VAC
RT1
t°
1
R1
68
Ω
LINE
J1-1
NTRL
RV1
275 VAC
C3
0.047
µF
X2
R7
1 kΩ
1N4007 x 4
C2
0.01
µF
1 kV
4
OPTIONAL
R16
2.0 kΩ R15
1% 2.4 kΩ
Q1
2SA0885
D8
1N4005
12
13
5 mH
CM Choke
+5 V, 2.5 A
J2-3
Q5
2N3906
L4
3.3
µH
Q4
2N3904
D5
1N4007GP
9
D10
SB540CT
D9
1N4005
+3.3 V, 2 A
J2-6
C12
1200
µF
10 V
10,11
R17
200
Ω
C18
470
µF
10 V
RET
R13
2 kΩ
1%
R12
6.34 kΩ
1%
R11
20.0 kΩ
1%
J2-2, 4, 5, 7
C9
150
µF
35 V
TOPSwitch-GX
U1
TOP245P
CONTROL
C
D
D12
UF4003
14
C13
47
µF
25 V
C16
0.1
µF
7
5
R3
270
Ω
Q3
1N3906
C6
150
µF
35 V
R8
1
Ω
1/2 W
-24 V, 50 mA
J2-1
U2
LTV817A
C14
R10
0.1
µF
10 kΩ
S
M
R2
18 kΩ
R4
10 kΩ
R6
5.1 kΩ
D6
1N4148
C5
47
µF
25 V
U3
TL431
R9
10.0 kΩ
1%
PI-3648-071106
Figure 1. 20 W Multiple Output DVD Supply.
DI-55
www.powerint.com
July 2006
POWERINT [ POWER INTEGRATIONS, INC. ]
