Page 37 - PEN eBook May 2023

DESIGN DESIGN

As technology evolved, smaller versions of the brick
package evolved, known as fractional bricks.
These ranged from a half-brick down to the
1/16 brick, although the size ratios are not exact. As
these footprints have become a de facto industry
standard, server design engineers can easily implement
these standardized brick packages during the design
process and users are able to multi-source with
relative ease, giving them assurance of supply.

However, with ability to radiate heat being linked
Fractional bricks are a range of power modules with de facto
industry-standard sizes and footprints. to physical size, there is a finite amount of energy
that can be removed from each size of brick. This is
Supporting 48-V practical due to the impact of power loss and voltage now the limiting factor in the amount of power that
each fractional brick form factor can deliver for a
given efficiency level. For example, we could assume
drops related to connections within and from the
Conversion in Data cabinet. that a quarter-brick could dissipate 25 W, which,
for example, corresponds to a 500-W device at 95%
efficiency. Increasing the power output to 900 W
Responding to this, in 2016, the Open Compute
Center Computing, Project (OCP) began to drive toward 48 V as a standard with the same 25-W loss would imply an efficiency of
97.3%.
for servers and distribution within data centers. The
choice of 48 V was to reduce current by a factor of
Today, we are at an inflection point in terms of the
Telecoms 4 (delivering a sixteen-fold reduction in I2R losses). relation between efficiency and power, with increases
Additionally, 48 V can be viewed as safer with
extra-low voltage (ELV) or separated extra-low voltage
in efficiency shifting from a relatively proportional
(SELV) depending on grounding, meaning that isolation to a more exponential relationship with power. Thus,
System architects are looking for improved can be removed from the power path, delivering a as efficiency rises toward 100%, each incremental
consequential efficiency increase.
improvement leads to a much more significant
power-conversion efficiencies that support higher The change to 48 V is reflected in the Open Rack improvement in power capability.

Many 48-V bricks include isolation as a result of their
rack-power ratings while driving down energy use, Base Specification, now at version 3 (ORv3). Alongside use in telecom systems. In these bricks, the 48-V
stipulations for the mechanical design of racks, this
minimizing thermal dissipation and reducing ongoing document defines voltage specifications for the input input rail has negative polarity, so galvanic isolation is
voltage (either 51 VDC or 54 VDC) as well as current
required to invert the output for positive polarity. For
operating costs. ratings for key components and the need for voltage 48 VDC, the server supply voltage is positive polarity;
sensing. It also specifies that the bus voltage remain
therefore, no inversion and no isolation is needed,
lower than the 60-VDC limit of ELV. as noted in the OCP proposals. The removal of the
By Andy Brown, director of technical marketing for DC/DC products for industrial requirement for isolation can yield an (approximate)
power at Advanced Energy At the same time, many areas of servers are heavily 0.3% improvement in overall efficiency, thereby
committed to 12 V—not least motherboards, PCIe slots, increasing the power capability of the brick.
memory and hard drives. Designs for 12 V are well
The requirements for powering a modern server are is to reduce the total cost of ownership of the entire understood and supply chains are fully established. Similarly, removing the output voltage regulation
largely defined by the computing capability of that system and increase the functionality and performance As a result, the need for a 12-V rail within mainstream from a brick converter can yield an (approximate) 0.5%
server. As the servers become more capable, their of the server. servers will continue for the foreseeable future. increase in efficiency. Given that the 48-VDC input
power requirements also increase. Efficiency is critical, voltage is comparatively tightly regulated, one might
as it not only reduces operating expenses but allows Traditionally, data center power solutions convert DELIVERING EFFICIENT 48-V TO 12-V assume this would be another realizable benefit.
for smaller power solutions with enhanced power incoming grid supply voltage to lower-voltage CONVERSION
density. three-phase mains voltage that is converted locally With many of the modern processors requiring up to For the majority of components, this would be true,
in rack-mounted servers to 12 VDC (the preferred 700–800 W of power, many power solutions for servers but memory (DIMMs) and PCIe cards require a highly
With high capital costs for equipment and space and voltage for many components, including motherboards tend to be in the 800-W to 1-kW region, with 900 W regulated 12-VDC supply, so being that a single brick is
rising energy costs, incremental efficiency gains make and peripherals like hard drives). However, with some being highly popular. Almost exclusively, 48-V to 12-V used for the 48-V:12-V conversion function, a regulated
a significant impact for server farms, where thousands 19-inch rack cabinets now requiring 30 kW, a 12-V conversion uses the so-called “brick”-derived form output remains by far the most sensible and popular
of servers are deployed simultaneously. Increased distribution voltage presents challenges for distributing factor. The term “brick” was coined over choice.
efficiency also reduces the load for air conditioning and converting power from AC/DC converters mounted 20 years ago to describe a PCB-mount package with
for cooling the building, saving capital and operating in a sub-rack, which is remote from the server. Current, an approximately 4.6 × 2.4-inch footprint. As servers become more sophisticated, so do the
expenses. Ultimately, the goal for any power solution for example, can reach 2,500 A, which is far from power solutions they rely upon. Many supplies now

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