TOP221-227

D

7/01

6

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.

Wide-Range

DC Input

D

S

C

CONTROL

PI-2115-040401

+

-

R3

47 k

Ω

D1

UF4005

C1

2.2 nF

1 kV

D2

UF5401

TOP221P

L1

3.3

D3

1N4148

C4

100

µF

16 V

U2

PC817A

R1

10

Ω

C3

100

µF

10 V

+5 V

C5

47

µF

10 V

C2

330

µF

10 V

U1

R2

100

Ω

VR1

TOPSwitch-II

T1

RTN

+

-

12 V Non-Isolated