Design Idea DI-30
®
TOPSwitch-GX
180 W PC Main SFX Supply
Application
PC Main
Device
TOP249Y
Power Output
180 W
Input Voltage
Output Voltage
Topology
Forward
90-130 VAC / 180-265 VAC 3.3 V / 5 V / 12 V / -12 V
®
Design Highlights
• 180 W cont. (200 W peak) in PC SFX form factor
• Includes passive power factor correction (PFC)
•
TOPSwitch-GX
integrated features enable extremely low
component count
• Meets 1 W standby spec (0.91 W input, 0.5 W output)
• High efficiency (71% minimum)
• Integrated line undervoltage and overvoltage detection
• Low EMI due to frequency jitter
• SOURCE referenced TO-220 tab lowers conducted EMI
• Maximum duty cycle reduction (DC
MAX
) prevents transformer
saturation for fault and transient loads
• Uses conventional magamp for 3.3 V output
• Meets CISPR22B/EN55022B conducted EMI
C3) balancing circuit, operating only as needed to minimize
zero-load power consumption.
Resistors R3, R5 and R6 implement start-up undervoltage
lockout, which prevents the supply from starting below
180 VDC. Components R4, R14, Q1 and R30 implement an
independent undervoltage using the X pin, which allows the
supply to continue delivering power all the way down to
140 VDC (increasing holdup time). Resistor R7 provides
additional hysteresis.
The primary side components D1, VR3-5 and C4, along with
secondary side C9 and R30, implement the Zener/capacitor
reset/clamp circuit. This circuit provides reset voltage for the
transformer and clamps the DRAIN pin voltage to a safe level
(<~600 V) under all conditions.
The reset circuit works in conjunction with the DC
MAX
reduction circuit (R8, R36, C22, VR19 and D18) to limit the
maximum duty cycle and prevent transformer saturation
under fault and transient conditions.
C10
1 nF
50 V
5
R1
330 kΩ
C4
2.2 nF
1 kV
D1
1N5407
2
R3
2.2 MΩ
R4
2.2 MΩ
R5
180 kΩ
1
14
D7
MBR3045
13
R30
1
Ω
1W
8, 9, 10
R6
2.2 MΩ
C20
330 pF
50 V
11,12
3
R13
10
Ω
D8
MBR6045
C12
2200
µF
6.3 V
R21
270
Ω
C9
47 nF
50 V
7, 8
Coupled
choke
L1
13
µH
Operation
TOPSwitch-GX
integrates many features designed for use with
forward converters. Passive power factor correction (PFC) is
implemented using inductors LPFC1 and LPFC2. Transistors
Q4, Q6, R1, R2, R3, R5, and R6 form an active capacitor (C2,
4
1, 2
C11
1000
µF
16 V
L2
0.5
µH
+12 V
6
3
+5 V
C13
220
µF
63 V
TO
MAGAMP OUT
(3.3 V)
RTN
C25
1
µF
50 V
LM
320
- 12 V
BR1
KBL06
CY3
2.2 nF
(Safety)
JP9
CX1
0.047
µF
250 VAC
L7
8.2 mH
CX2
0.33
µF
250V
RT1
10
Ω
R10
560 K
1/2 W
LPFC1
C2
470
µF
200 V
Q4
MPSA42
LPFC2
CY4
2.2 nF
(Safety)
Q6
MPSA92
To AC Selector
Switch
VR3
BZY97C-
200
VR4
BZY97C-
180
VR5
BZY97C-
R2
180
330 kΩ
D
L
CONTROL
C
TOPSwitch-GX
U1
TOP249
R8
130 kΩ
1%
R36
43.2 kΩ
1%
C22
100 pF
50 V
R7
560 kΩ
D6
BAV20
D18
BAV20
4
C5
1
µF
100 V
C27
330 pF
50 V
R11
330
Ω
D20
UF4002
C24
330
µF
25 V
R18
4.74 kΩ
1%
R15
1.8 kΩ
C17
100 nF
50 V
R16
1 kΩ
C16
100 nF
R17
50 V
15 kΩ
VR19
1N5229
C3
470
µF
200 V
R20
270 kΩ
S
X
F
C8
0.033
µF
50 V
R9
47
Ω
C6
47
µF
16 V
R11
300
Ω
Q1
2N3908
R14
75 kΩ
D105
1N4148
U2
SFH615A-2
RV1
275 V, 14 mm
R30
3.3 kΩ
U5
TL431
R19
4.12 kΩ
1%
PI-3384-120902
R12
12 kΩ
+12 V STBY
R38
5.1 kΩ
U3
LTV817
R106
27 kΩ
Remote
ON/OFF
R37
10 kΩ
F1
4A
L
G
N
C7
100 nF
50 V
Q7
2N3904
C23
33 nF
50 V
Figure 1.
180 W (200 W pk.) PC Main Power Supply Schematic (Note: Schematic does not include transformer Y-capacitor)
.
DI-30
www.powerint.com
December 2002
POWERINT [ POWER INTEGRATIONS, INC. ]
