
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