TOP221-227
L1
3.3µH
D2
UF5401
+5V
C2
C3
+
330 µF
100 µF
R3
47K
C1
2.2 nF
1KV
VR1
10V
10V
RTN
D1
UF4005
R2
100 Ω
D3
IN4148
R1
10 Ω
Wide-Range
DC Input
T1
+
U1
C4
100 µF
16V
D
TOP221P
TOP S w it c h -II
CONTROL
C
U2
PC817A
12V Non-Isolated
C5
47 µF
10V
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. RefertotheDataBookandDesignGuidefor
additional examples.
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.
4W Stand-by Supply using 8 Lead PDIP
The output voltage (5V) is directly sensed by the zener diode
(VR1)andtheoptocoupler(U2). Theoutputvoltageisdetermined
by the sum of the zener voltage and the voltage drop across the
LEDoftheoptocoupler(thevoltagedropacrossR1isnegligible).
The output transistor of the optocoupler drives the CONTROL
pinoftheTOP221. C5bypassestheCONTROLpinandprovides
control loop compensation and sets the auto-restart frequency.
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.
Thetransformer’sleakageinductancevoltagespikesaresnubbed
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.
For this application the input rectifiers and input filter are sized
for the main supply and are not shown. The input DC rail may
C
6
12/97
POWERINT [ Power Integrations ]
