April 2002

1/11

G. Augustoni - F. Salanitri

AN1484

APPLICATION NOTE

A 3.6 WATTS TRAVEL ADAPTOR USING VIPer12A

®

Abstract

The VIPer12A is an integrated PWM and MOSFET

circuit for low power application in the 5W range,

typically in Cellular Phone Adapters. It is housed in

surface mount SO-8 and DIP8 packages.

With the availability of VIPer12A in SO-8 package

and the limited number of external components for

a real PWM operation, building a compact and

performant power supply becomes simple.

The travel adaptor design presented here, has

been made with the aim of minimising overall cost

for a secondary voltage and current regulated

adapter, topology widely used in Cellular Phone

Adapters.

The VIPer12A presents itself as the answer for

lower consumption in standby, like in home

appliances where it will be required to limit non

negligible

"off

the

use"

consumptions,

as

recommended by the “European Commission of

Energy”. Today regulations demand less than 1

Watt. Thanks to VIPer12A low power consumption,

it is possible to achieve 100mW standby power in

a wide range of operations.

1.0 PRINCIPLE OF OPERATION

The circuit is a standard Flyback converter with

secondary current and voltage regulation driving

the

VIPer12A

feedback

pin

through

an

optocoupler.

Table 1: System Performances

1.1 The VIPer12A

1.1.1 Start-up phase

VIPer12A, as any member of the VIPer family, has

an integrated high voltage current source to charge

C3 Vdd capacitor until it reaches its startup level

(15V). When Vdd gets to 15V, the VIPer switches,

supplied by the energy stored in C3, until it is

supplied through the auxiliary winding.

1.1.2 Auxiliary Supply

VIPer12A has a wide operating voltage range from

9V to 40V, respectively maximum and minimum

values

for

undervoltage

and

overvoltage

protections. This wide voltage supply range

simplifies the design of the VIPer12A supply but, to

ensure proper operation of the application in any

case, it is advised:

- in normal operation, to supply VIPer12A within its

operating range;

-

in

standby

mode,

to

minimize

auxiliary

consumption to achieve very low standby power;

- in short circuit, to limit output power by going into

an hiccup mode;

- in constant current mode, to ensure current

regulation below 2V before going into hiccup

mode.

Parameters

100VDC

380VDC

Standby Power

90mW

119mW

Efficiency at 3.6W

62%

66%

Short Circuit Power

1W

1.3W

Load Regulation

3%

2%