Application Bulletin AB-28

Power Conversion for the Data

Communications Market

www.fairchildsemi.com

REV. 1.0.0

1

Abstract

This application bulletin discusses the transition from tradi-

tional telephony to converged voice and data over Internet

Protocol (IP) and its implications for the power conversion

of such systems. A few power conversion examples are pro-

vided complete of applications schematics.

Introduction

The arm wrestling between voice and data has concluded in

favor of the latter with all the major players now posturing

for leadership of the migration from traditional voice to

Internet Protocol (IP) telephony. On the short term the huge

investments in both traditional telephony infrastructure and

data over IP warrants that over the next few years we will

have to provide power conversion for both types of systems

as well as for the converged systems to come.

Current Environment with Separate

Networks

Fig. 1 shows the current situation with voice going through

traditional PBX (Private Branch Office), Central Office, and

Switch to the Public Switch Telephone Network (PSTN). On

independent paths the data travels from Routers to wide Area

Networks (WAN) and the video goes trough a third indepen-

dent path.

Fig.1. Separate Networks for Voice, Data and Video

Migration to Converged Voice/

Data IP

Fig. 2 shows the envisioned converged Voice/Data/Video

system over IP. At the center of this new universe is the

Internet Protocol Wide Area Network, with all the services,

including voice, data, video and wireless communications

gravitating around it.

Fig. 2. Voice/Data/video Over IP

Telecom –48V DC Power Distribution

Traditionally telecom systems have been distributing a DC

power (-48V typically) obtained from a battery back up

being continually charged by a Rectifier/Charger from the

AC line. Subsequently the –48V is converted into various

low positive DC voltages (Fig. 3 shows 12V only for

simplicity) as well as back to AC voltages as necessary.

Fig. 3. Telecom –48V DC power distribution

Datacom AC Power Distribution

Data centric systems tend to rely on an Uninterruptible

Power Supply (AC UPS) front-end for distributing AC

power, which subsequently is converted into the basic

constituents, -48V, AC power and low voltage DC (again,

for simplicity we are only showing a 12V DC in Fig. 4).

Home

Phone/Fax

Wide Area

Network

(WAN)

Router

Video

Video

Video

Voice

Switch

Central

Office

Data

Office PBX

(Private Branch

Exchange)

Public Switch

Telephone

Network (PSTN)

Video

Router

WLAN

IPWAN = Internet Protocol Wide Area Network

WLAN = Wireless Local Area Network

PSTN = Public Switched Telephone Network

IP WAN

PSTN

DC/AC

DC/DC

Battery

Backup

Rectifier

/Charger

-48V

AC LINE

12V DC

-48V

120/208V AC