Rev. G 08/16

6

TOP221-227

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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 volt-

age 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 com-

pensation 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-isolat-

ed 12 V output which is also used to bias the collector of the

optocoupler’s output transistor. The isolated 5 V output wind-

ing 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

µH

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