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Front End vs. Rectifier Comparison
Page 1 of 3
Comparison of Front-End
Power Supplies to Rectifier Modules
Introduction
How does a front-end power supply differ from a
rectifier module? Though similar, there are subtle
differences between these two kinds of power
supplies, and these differences need to be
understood before the most-appropriate power
system can be configured.

Front-End Power Solutions
The input of a front-end is connected to an AC
voltage, and its output is a regulated DC bus voltage.
This bus voltage, commonly 12V, 24V, or 48V is
typically used to power other DC-DC converters;
however, its important to note that front-ends
should not be used in applications where
batteries are to be charged and monitored.

Batteries require sophisticated charging circuitry, and
front-end supplies do not have this capability.

Markets Served by Front-Ends Networking
equipment/datacom Enclosures / Cabinet power Data
storage Data
Centers Blade
Servers
The AC input voltage range for a front-end is typically
from 87 VAC to 264 VAC, and front-ends will usually
be powered from a single-phase input. Some front-
ends can be operated from a DC source; however,
the AC input version is much more common. The
connection to the AC input voltage is usually located
at one end of the power supply chassis, while the
connection for the output DC bus voltage is located at
the opposite end of the power supply. The AC input
connector, e.g., an IEC-type AC plug, is usually
located at the front of the supply, and the DC output
is located at the rear. PowerOne also offers a
family of AC front-ends whose input and output
connectors are located on the same end.
The typical output power rating of an individual front-
end ranges from 300 watts to 1800 watts. Cooling is
provided by internal fans, and the direction of airflow
is usually from front-to-rear, although models with
reverse airflow are available. All front-end supplies
from Power-One incorporate internal ORing FETs
and employ a droop method technique for current
sharing.




Power-One FNP1800, 1800-Watt Front-End


Front-ends are often mounted into a power shelf,
such as the one shown below, that accommodates
more than one front-end when additional or
redundant power is needed.





Power-One's FNR-3 Shelf provides
up to 5400 Watts in a 1U-High, 19" Rack
The typical operating ambient temperature range of a
front-end is 0 to 50 ºC. These supplies can be
operated in ambient temperatures exceeding 50 ºC;
however, the output power will usually begin to
derate above 50 ºC. The maximum operating temp-
erature for front-ends is usually 70 ºC., and the
common derating from 50 ºC. to 70 ºC. is 2.5% / ºC,
such that the supply will provide 50% of its rated
output current at 70 ºC.
Status information is provided from the front panel
LEDs, logic signals, and via the I
2
C management
interface. The I
2
C bus can also enable the power
supply, control fan speed, and adjust the output
voltage. Status LEDs give indications of the input
voltage, the output voltage, and the presence of an
overtemperature condition.

Rectifier Modules in a DC Power System
A typical DC Power System is comprised of a
minimum of four components: rectifier modules, a
controller/supervision module, and distribution
modules mounted in one or more power shelves.
Batteries are often part of a DC Power System, as
well. Rectifier modules are similar to front-ends, but
there are important differences. Perhaps the most
notable difference is that rectifier modules, when
used in conjunction with a controller/supervisor
module, provide sophisticated battery management
to adjust their output voltage as required for charging
batteries. In general, a rectifier module and assoc-
iated power system could be used in a front-end
application, but a front-end could not be used in a
DC Power System application that requires battery
management.
The AC input and DC output connectors are both
located at the rear of a rectifier module. The rectifier
modules regulated output bus voltage is typically +24
VDC (27.25 VDC float voltage), or -48 VDC (-54.5
VDC float voltage), with -48 VDC being the most
prevalent. Rectifier module cooling is usually
provided by internal fans, and the airflow direction is
typically from front to rear. Natural convention-cooled
Page 2 of 3
Comparison of Front-End
Power Supplies to Rectifier Modules
rectifier modules are also available. The operating
temperature range of todays DC Power Systems will
often be from -40 ºC to 65 ºC with no derating at the
complete operating temperature range. Derating will
occur between 65 ºC. and 75 ºC. All the rectifiers
incorporate internal ORing FETs and employ an
active technique for current sharing. Virtually any
number of AC rectifiers can be operated in a parallel
mode.
Rectifier modules are available in many output power
ratings, from 400 watts to several kilowatts. Power-
One offers the Magnum REC-J200EH, a 3U-High, 12
kW rectifier module which can be used as a building
block in an 800 kW Power System. The basic
functionality of the individual components of a DC
Power System is the same, regardless of the total
system power.




XR04.48/XR08.48
1U-High Rectifier Module (400 Watts / 800 Watts)








Aspiro
TM
Shelf System comprised of a PCC
Super-vision Module, Two (2) XR04.48/XR08.48
Rectifier Modules, and a front-access, 5-position
Fuse Distribution Module

The PCC (prime controller card) Supervision Module
in the Power System shown above performs several
functions. This module is a pluggable micro-
processor controller that monitors all system
parameters including DC voltage, rectifier current,
rectifier temperature, system capacity, battery
information, and circuit breaker status. Alarm and
warning notifications are indicated on the front panel
by LEDs and through potential free alarm contacts
that allow remote signaling. External user-selectable
alarm parameter monitoring is accomplished through
an RS232 port using PC-based PowCom Software.
The PCC controller can also provide a wide variety
of intelligent battery management, such as: low-
voltage disconnect, temperature compensation with
programmable compensation factor, automatic and
manual load testing, load shedding, and monitoring
of remaining battery capacity.



Typical Output Rating of DC Power Systems By End-Application
Micro <3 kW
Small <18 kW
Medium <400 kW
Large <800 kW Broadband
access Data
networks
Wireless Base Stations Enterprise Wireless Base Stations Transmission Central
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Centers Mobile Switch Sites Distributed
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Centers Mobile Switch Sites
































Page 3 of 3
Comparison of Front-End
Power Supplies to Rectifier Modules


The table below compares various parameters of
front-end power supplies and rectifiers. General
comparisons were done using Power-Ones
FNP600-48 front-end and the XR04.48/XR08.48
rectifiers.






Rectifier Front-End Comparison
Description Front-End Rectifier Comments
Input voltage range
85 to 264 VAC; 300 VAC for
60 ms
85 to 300 VAC; 300 VAC
continuous; >315 VAC
disconnect

Output voltage range
48V
±
8% (margin/I
2
C).
Not designed for battery
charging.
44V to 57.5V
(temperature/RS485).
Designed to adjust output
voltage for battery
management.

AC input, DC output locations AC input available on either
front or rear; DC output
always on rear.
AC input and DC output
always on rear of AC rectifier.
No input/output connection
options on rectifier
Input overvoltage protection
VDR, immunity level 3
VDR, NEBS, input
overvoltage disconnection,
immunity levels 3 & 4, high
surge current protection
(5 kA)
Disconnect relays require
special circuit in rectifiers
Input fuse
1 fuse
2 fuses

Turn-on behavior
Continuous rise to nominal
output voltage
Specific walk-in profile due to
possible battery