TOP221-227

C

12/97

6

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.

Wide-Range

DC Input

D

S

C

CONTROL

PI-2115-111797

+

-

R3

47K

D1

UF4005

C1

2.2 nF

1KV

D2

UF5401

TOP221P

L1

3.3

µH

D3

IN4148

C4

100

µF

16V

U2

PC817A

R1

10

Ω

C3

100

µF

10V

+5V

C5

47

µF

10V

C2

330

µF

10V

U1

R2

100

Ω

VR1

TOPSwitch-II

T1

RTN

+

-

12V Non-Isolated