TOP221-227
D2
UF5401
L1
3.3µH
+5V
C3
100
µF
10V
RTN
+
R3
47K
C1
2.2 nF
1KV
D1
UF4005
C2
330
µF
10V
VR1
R2
100
Ω
D3
IN4148
T1
R1
10
Ω
Wide-Range
DC Input
D
U1
TOP221P
CONTROL
TOPSwitch-II
C
C4
100
µF
16V
C5
47
µF
10V
U2
PC817A
+
12V Non-Isolated
S
-
-
PI-2115-111797
Figure 7. Schematic Diagram of a 4W TOPSwitch-II Stand-by Power Supply using an 8 lead PDIP.
Application Examples
Following are just two of the many possible
TOPSwitch
implementations. Refer to the Data Book and Design Guide for
additional examples.
4W Stand-by Supply using 8 Lead PDIP
Figure 7 shows a 4W stand-by supply. This supply is used in
appliances where certain stand-by functions (e.g. real time
clock, remote control port) must be kept active even while the
main power supply is turned off.
The 5V secondary is used to supply the stand-by function and
the 12V non-isolated output is used to supply power for the
PWM controller of the main power supply and other primary
side functions.
For this application the input rectifiers and input filter are sized
for the main supply and are not shown. The input DC rail may
vary from 100V to 380V DC which corresponds to the full
universal AC input range. The TOP221 is packaged in a 8 pin
power dip package.
The output voltage (5V) is directly sensed by the zener diode
(VR1) and the optocoupler (U2). The output voltage is determined
by the sum of the zener voltage and the voltage drop across the
LED of the optocoupler (the voltage drop across R1 is negligible).
The output transistor of the optocoupler drives the CONTROL
pin of the TOP221. C5 bypasses the CONTROL pin and provides
control loop compensation and sets the auto-restart frequency.
The transformer’s leakage inductance voltage spikes are snubbed
by R3 and C1 through diode D1. The bias winding is rectified
and filtered by D3 and C4 providing a non-isolated 12V output
which is also used to bias the collector of the optocoupler’s
output transistor. The isolated 5V output winding is rectified by
D2 and filtered by C2, L1 and C3.
6
C
12/97
POWERINT [ POWER INTEGRATIONS, INC. ]
