TOP232 datasheet(16/38 Pages) POWERINT

16 / 38 page

Rev. D 10/20

TOP232-234

www.power.com

17 W PC Standby Power Supply

Figure 26 shows a 17 W PC standby application with 3.3 V

and 5 V secondary outputs and a 15 V primary output. The

supply uses the TOP232 operating from 230 VAC or 100/

115 VAC with doubler input. This design takes advantage of

the soft-start, line under-voltage detect, tighter current limit

variation and higher switching frequency features of

TOPSwitch-FX. For example, the higher switching frequency

with tighter current limit variation allows use of an EE19

transformer core. Furthermore, the spacing between high-

voltage DRAIN pin and low voltage pins of the TOPSwitch-FX

packages provides large creepage distance which is a

significant advantage in high pollution environments such as

fan cooled PC power supplies.

Capacitor C1 provides high frequency decoupling of the

high-voltage DC supply, and is necessary only if there is a long

trace length from the source of the DC supply to the inputs of

this standby circuit. The line sense resistor R1 senses the DC

input voltage for line undervoltage. When AC is turned off, the

under-voltage detect feature of the TOPSwitch-FX prevents

auto-restart glitches at the output caused by the slow

discharge of large storage capacitance in the main converter.

This is achieved by turning the power supply off when the

input voltage goes below a level needed to maintain output

regulation and keeping it off until the input voltage goes above

the under-voltage threshold (V

UV), when the AC is turned on

again. The under voltage threshold is set at 200 VDC, slightly

below the required lowest operating DC input voltage, for

start-up at 170 VAC. This feature saves several components

needed to implement the glitch free turn off with discrete or

TOPSwitch-II based designs.

The bias winding is rectified and filtered by D2 and C6 to

create a bias voltage for the TOP232 and to provide a 15 V

primary bias output voltage for the main power supply primary

control circuitry. Both 3.3 V and 5 V output voltages are

sensed by R9, R10 and R11 using a TL431 (U3) circuit shown.

Resistor R6 limits current through optocoupler U2 and sets

overall AC control loop gain. Resistor R7 assures that there is

sufficient bias current for the TL431 when the optocoupler is at

a minimum current. Capacitor C8 provides a soft-finish

function to eliminate turn-on overshoot. The no load regulation

(cycle-skipping) of TOPSwitch-FX permits the circuit to meet

the low standby power requirement of the Blue Angel

specification for PCs.

Figure 26. 17 W PC Standby Supply.

3.3 V

@ 2 A

200 - 375

VDC

BAV21

µF

35 V

C11

100

µF

10 V

µF

SFH615-2

TL431CLP

0.1

µF

301

Ω

16.2 k

Ω

UF4005

VR1

BZY97C-

200

TOP232Y

TOPSwitch-FX

510

Ω

0.01

µF

1 kV

(optional)

(Primary

Referenced)

35 V

SB540

5 V

@ 2 A

C12

1000

µF

10 V

C10

1000

µF

10 V

CY1

1 nF

–

PI-2537-062515

RTN

15 V

@ 30 mA

6.8

Ω

3.9 M

Ω

3.3

µH

3.3

µH

R10

12.1 k

Ω

R11

10 k

Ω

C13

100

µF

10 V

CONTROL

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