®
Design Idea DI-30
TOPSwitch®-GX
180 W PC Main SFX Supply
Topology
Device
Output Voltage
Application
Power Output
Input Voltage
Forward
PC Main
3.3 V / 5 V / 12 V / -12 V
180 W
90-130 VAC / 180-265 VAC
TOP249Y
C3) balancing circuit, operating only as needed to minimize
zero-load power consumption.
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)
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.
• Integrated line undervoltage and overvoltage detection
• Low EMI due to frequency jitter
• SOURCE referenced TO-220 tab lowers conducted EMI
• Maximumdutycyclereduction(DCMAX)preventstransformer
saturation for fault and transient loads
• Uses conventional magamp for 3.3 V output
• Meets CISPR22B/EN55022B conducted EMI
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
transformerandclampstheDRAINpinvoltagetoasafelevel
(<~600 V) under all conditions.
Operation
The reset circuit works in conjunction with the DCMAX
reduction circuit (R8, R36, C22, VR19 and D18) to limit the
maximum duty cycle and prevent transformer saturation
under fault and transient conditions.
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,
C10
1 nF
50 V
Coupled
choke
L1
13 µH
5
4
+12 V
+5 V
14
MBR3045
13
2
C11
1, 2
C4
7, 8
D7
R3
1000 µF
16 V L2
R1
2.2 nF
2.2 MΩ
330 kΩ
C9
47 nF
50 V
1 kV
R4
0.5 µH
2.2 MΩ
6
3
R5
180 kΩ
D1
1N5407
R30
1 Ω
1 W
BR1
KBL06
Q4
MPSA42
1
C13
C2
220 µF
C12
470 µF
200 V
R21
270 Ω
8, 9, 10
63 V
D8
2200 µF
LPFC1
CY3
2.2 nF
(Safety)
MBR6045
6.3 V
C20
TO
R6
2.2 MΩ
330 pF
MAGAMP OUT
50 V
(3.3 V)
RTN
11,12
LPFC2
CY4
2.2 nF
(Safety)
C24
330 µF
25 V
JP9
TOPSwitch-GX
C27
D6
BAV20
3
4
330 pF
50 V
R13
10 Ω
U1
C5
C25
TOP249
1 µF
R18
1 µF
CX1
D18
BAV20
100 V
R11
330 Ω
4.74 kΩ
1%
R15
1.8 kΩ
Q6
MPSA92
50 V
R36
43.2 kΩ
1%
R8
130 kΩ
1%
0.047 µF
LM
- 12 V
250 VAC
320
To AC Selector
Switch
D20
L7
8.2 mH
UF4002
VR19
1N5229
R7
560 kΩ
D
S
L
C22
100 pF
50 V
VR3
BZY97C-
200
C17
100 nF
50 V
R20
270 kΩ
CX2
0.33 µF
250V
CONTROL
C3
470 µF
200 V
C
R16
U2
SFH615A-2
VR4
BZY97C-
180
R11
1 kΩ
R10
560 K
1/2 W
300 Ω
RT1
10 Ω
C8
C16
X
F
R9
47 Ω
0.033 µF
100 nF R17
Q1
2N3908
50 V
50 V 15 kΩ
VR5
BZY97C-
180
RV1
275 V, 14 mm
R2
330 kΩ
D105
R30
3.3 kΩ
1N4148
C6
47 µF
16 V
R14
75 kΩ
U5
TL431
R19
4.12 kΩ
1%
PI-3384-120902
+12 V STBY
R12
12 kΩ
R106
27 kΩ
R38
5.1 kΩ
Remote
ON/OFF
U3
LTV817
F1
4 A
C7
100 nF
50 V
Q7
2N3904
C23
33 nF
50 V
R37
10 kΩ
L
G
N
Figure 1. 180 W (200 W pk.) PC Main Power Supply Schematic (Note: Schematic does not include transformer Y-capacitor).
December 2002
DI-30
www.powerint.com
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