Design Idea DI-20
®
TOPSwitch-GX
145 W PC Main ATX Supply
Application
PC Main
Device
TOP247
Power Output
145 W
Input Voltage
90-130 VAC / 180-265 VAC
Output Voltage
3.3 V / 5 V / 12 V
Topology
Forward
®
Design Highlights
• 145 W cont. (160 W peak) in PC ATX form factor
•
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 (DC
MAX
) reduction prevents transformer
saturation for fault and transient loads
• Uses conventional magamp for 3.3 V output
• Meets CISPR22B/EN55022B conducted EMI
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 hold-up 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
4
Coupled
choke
L1
13
µH
Operation
TOPSwitch-GX
integrates many features designed for use with
forward converters. Transistors Q4, Q6, R1, R2, R3, R5 and R6
form an active capacitor (C2, C3) balancing circuit, operating
3
1, 2 C11
1000
µF
16 V
R1
330 kΩ
C4
2.2 nF
1 kV
D1
1N5407
1
R3
2.2 MΩ
R4
2.2 MΩ
R5
180 kΩ
5
14
D7
MBR3045
13
R30
1
Ω
1W
8, 9
D8
MBR6045
C9
47 nF
50 V
+12 V
L2
0.5
µH
+5 V
5, 6
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
CY4
2.2 nF
(Safety)
C2
330
µF
200 V
Q4
MPSA42
C12
2200
µF
6.3 V
R6
2.2 MΩ
C20
330 pF
50 V
11,12
7
R13
10
Ω
R21
270
Ω
C13
220
µF
63 V
TO
MAGAMP
(3.3 V)
RTN
TOPSwitch-GX
U1
TOP247
To AC Selector
Switch
Q6
MPSA92
R8
130 kΩ
1%
D
L
CONTROL
C
D6
BAV20
D18
BAV20
R36
43.2 kΩ
1%
C22
100 pF
50 V
R7
560 kΩ
3
C5
1
µF
100 V
R18
4.74 kΩ
1%
C17
100 nF
50 V
U2
SFH615A-2
R16
1 kΩ
R15
1.8 kΩ
R20
270 kΩ
C3
330
µF
200 V
VR3
BZY97C-
200
VR4
BZY97C-
180
VR5
R2
BZY97C-
330 kΩ
180
VR19
1N5229
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
U5
TL431
C16
100 nF
R17
50 V
15 kΩ
RV1
275 V, 14 mm
R30
3.3 kΩ
R19
4.12 kΩ
1%
PI-3165-120902
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.
145 W (160 W pk.) PC Main Power Supply Schematic (Note: Schematic does not include transformer Y-capacitor).
DI-20
www.powerint.com
December 2002
POWERINT [ POWER INTEGRATIONS, INC. ]
