TOP221-227
D2
UF5401
L1
3.3
µH
+5 V
C3
100
µF
10 V
RTN
+
R3
47 kΩ
C1
2.2 nF
1 kV
D1
UF4005
C2
330
µF
10 V
VR1
R2
100
Ω
D3
1N4148
T1
R1
10
Ω
Wide-Range
DC Input
D
U1
TOP221P
CONTROL
TOPSwitch-II
C
C4
100
µF
16 V
C5
47
µF
10 V
U2
PC817A
+
12 V Non-Isolated
S
-
-
PI-2115-040401
Figure 7. Schematic Diagram of a 4 W TOPSwitch-II Standby 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.
4 W Standby Supply using 8 Lead PDIP
Figure 7 shows a 4 W standby supply. This supply is used in
appliances where certain standby functions (e.g. real time
clock, remote control port) must be kept active even while the
main power supply is turned off.
The 5 V secondary is used to supply the standby function and
the 12 V 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 100 V to 380 V DC which corresponds to the full
universal AC input range. The TOP221 is packaged in an 8 pin
power DIP package.
The output voltage (5 V) 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 12 V output
which is also used to bias the collector of the optocoupler’s
output transistor. The isolated 5 V output winding is rectified by
D2 and filtered by C2, L1 and C3.
6
D
7/01
POWERINT [ POWER INTEGRATIONS, INC. ]
