TOP232-234 Datasheet, PDF (16/36 Pages) Power Integrations, Inc. – Family Design Flexible,EcoSmart, Intergrated OFff-line Switcher

TOP232-234
17 W PC Standby Power Supply
Figure 26 shows a 17 W PC standby application with 3.3 V and
5 V secondary outputs and a 15 V primary output. The supply
uses the TOP232 operating from 230 VAC or 100/115 VAC
with doubler input. This design takes advantage of the soft-
start, line under-voltage detect, tighter current limit variation
and higher switching frequency features of TOPSwitch-FX. For
example, the higher switching frequency with tighter current
limit variation allows use of an EE19 transformer core.
Furthermore, the spacing between high voltage DRAIN pin and
low voltage pins of the TOPSwitch-FX packages provides large
creepage distance which is a significant advantage in high
pollution environments such as fan cooled PC power supplies.
Capacitor C1 provides high frequency decoupling of the high
voltage DC supply, and is necessary only if there is a long trace
length from the source of the DC supply to the inputs of this
standby circuit. The line sense resistor R1 senses the DC input
voltage for line under-voltage. When AC is turned off, the
under-voltage detect feature of the TOPSwitch-FX prevents
auto-restart glitches at the output caused by the slow discharge
of large storage capacitance in the main converter. This is
achieved by turning the power supply off when the input
voltage goes below a level needed to maintain output regulation
and keeping it off until the input voltage goes above the
under-voltage threshold (V_UV), when the AC is turned on again.
The under voltage threshold is set at 200VDC, slightly below
the required lowest operating DC input voltage, for start-up at
170VAC. This feature saves several components needed to
implement the glitch free turn off with discrete or
TOPSwitch-II based designs.
The bias winding is rectified and filtered by D2 and C6 to create
a bias voltage for the TOP232 and to provide a 15V primary
bias output voltage for the main power supply primary control
circuitry. Both 3.3V and 5V output voltages are sensed by R9,
R10 and R11 using a TL431 (U3) circuit shown. Resistor R6
limits current through optocoupler U2 and sets overall AC
control loop gain. Resistor R7 assures that there is sufficient
bias current for the TL431 when the optocoupler is at a minimum
current. Capacitor C8 provides a soft-finish function to eliminate
turn-on overshoot. The no load regulation (cycle-skipping) of
TOPSwitch-FX permits the circuit to meet the low standby
power requirement of the Blue Angel specification for PCs.
+
200-375
VDC
C1
0.01 µF
1 kV
(optional)
-
CY1
1 nF
L1
3.3 µH
VR1
BZY97C-200
R1
3.9 MΩ
D1
UF4005
D
U1
TOP232Y
S
D3
SB540
D4
SB540
C10
1000 µF
10 V
C12
1000 µF
10 V
D2
BAV21
T1
M TOPSwitch-FX
CONTROL
C
R5
F
6.8 Ω
C5
47 µF
C6
35 V
R6
301 Ω
C8
10 µF
35 V
L2
3.3 µH
C11
100 µF
10 V
C13
100 µF
10 V
R7
510 Ω
U2
SFH615-2
C7
0.1 µF
U3
TL431CLP
R9
16.2 kΩ
R10
12.1 kΩ
R11
10 kΩ
Figure 26. 17 W PC Standby Supply.
5V
@2A
3.3 V
@2A
RTN
15 V
@ 30 mA
(Primary
Referenced)
PI-2537-040401
16 B
7/01