Design Idea DI-55
®
TOPSwitch-GX
20 W (25 W peak) DVD Supply
Application
Device
Power Output
Input Voltage
Output Voltage
Topology
DVD
TOP245P
20 W (25 W pk)
85-265 VAC
3.3 V / 5 V / 12 V / -24 V
Flyback
TheexternalcurrentlimitprogrammingandremoteON/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.
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
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.
• 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)
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.
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.
VR1
P6KE
130
C1
C4
33 µF
400 V
C8
L5
BEAD
L2
3.3 µH
33 µF
400 V
2.2 nFY1
+12 V, 500mA
T1
EE25L
F1
3.15 A
250 VAC
1
8
D7
L1
RT1
t°
1N5819
R1
J1-2
68 Ω
C15
470 µF
25 V
C20
LINE
180 µF
OPTIONAL
C2
RV1
275 VAC
25 V
C3
0.047 µF
X2
0.01 µF
12
13
C17
470 µF
10 V
1 kV
R14
1.13 kΩ
1%
R16
R7
1 kΩ
L3
3.3 µH
J1-1
R15
2.4 kΩ
Q1
1N4007 x 4
2.0 kΩ
5 mH
+5 V, 2.5 A
J2-3
1%
2SA0885
4
CM Choke
NTRL
D11
SB540CT
D8
1N4005
C12
Q5
2N3906
1200 µF
Q4
2N3904
10 V
D9
1N4005
L4
3.3 µH
D10
SB540CT
D5
+3.3 V, 2 A
J2-6
9
1N4007GP
C18
470 µF
10 V
C12
1200 µF
10 V
R17
200 Ω
RET
10,11
R13
J2-2, 4, 5, 7
2 kΩ
1%
C9
C6
R11
20.0 kΩ
1%
R12
150 µF
35 V
150 µF
6.34 kΩ
35 V
1%
R8
D12
UF4003
14
TOPSwitch-GX
1 Ω
U1
1/2 W
-24 V, 50 mA
J2-1
TOP245P
D
S
C13
47 µF
25 V
7
C16
0.1 µF
CONTROL
C
5
LTV817A
U2
M
R2
18 kΩ
R3
270 Ω
C14
0.1 µF
R10
10 kΩ
Q3
1N3906
R4
10 kΩ
R6
5.1 kΩ
C5
47 µF
25 V
D6
1N4148
U3
TL431
R9
10.0 kΩ
1%
PI-3648-071106
Figure 1. 20 W Multiple Output DVD Supply.
July 2006
DI-55
www.powerint.com