Page 16 - PEN Ebook March 2021

POWER SUPPLY Power Supply
GaN Technology for
Data Center
By Stephen Oliver, VP Corporate Marketing & Investor Relations, Navitas
Semiconductor
In part I, we looked at data center architectures
and introduced gallium nitride (GaN) power ICs and
their role in the second revolution in power elec-
tronics. Now, let’s look at GaN-enabled high-effi-
ciency hardware within the data center itself.
GAN WITH AC INPUT
For a traditional AC-in architecture, GaN can
be employed in high-frequency, soft-switch-
ing topologies. For the power factor correction
(PFC) stage, the traditional hard-switching,
low-frequency (47 kHz) boost is upgraded to a
soft-switching MHz ‘totem-pole’, and the DC-DC
stage upgraded in similar fashion. An example of
an ‘all GaN’ 3.2 kW approach is shown in figure
1, with a MHz totem-pole PFC followed by MHz
LLC. Navitas 650 V GaN is used for the PFC and
16 MARCH 2021 | www.powerelectronicsnews.com
DC-DC primary, with EPC 80 V GaN for the DC-DC
secondary side rectification. The design meas-
ures just 1U x 2U x 210 mm (800 cc) and achieves
power density of 4 W/cc (65 W/in3).
In industry, Eltek (Delta Electronics) announced
the 3 kW Flatpack2 SHE in 2017 ; the first in a
series of GaN-based AC-48/54/60 V power sup-
plies which achieve 98% efficiency and a 50%
reduction in loss vs. earlier silicon converters.
GAN WITH 400 V (HVDC) INPUT
DC
For HVDC, the essential equation derived from
Ohm’s Law is “Power loss = I R” so for each dis-
2
tribution network or connector, maintaining as
high a voltage as possible minimizes the current
for a given power, and so reduces loss. The con-
Figure 1: 3.2 kW AC-54V converter; 650V GaNFast power ICs
for MHz totem-pole PFC and MHz LLC primary with 100V
GaN FETs for LLC secondary rectification. [North Carolina
State University and University of Texas, Austin].
cept of HVDC in the data center is not new; with
work by NTT back in 1999 , and followed-up by
Lawrence Berkley National Labs in 2006 and Intel
in 2007 . However, the data center market is con-
servative, and change happens slowly. Adoption
is being accelerated by factors like the cost of
electricity (in $/kWhr), adherence to the ‘net-ze-
ro’ carbon emissions goal of the Paris Accord,
and using new technology to amplify the advan-
tages of architecture changes, i.e. Si-to-GaN.
For an HVDC network, we can use the post-PFC
DC-DC ‘back-end’ of a traditional AC-48 V sup-
DC
ply or turn to a more optimized, more granular
approach where power can be converted in inte-
gers of 300 W (or similar) and be located at the
closest point to the load(s) – thus maximizing
the longest path at the highest voltage.
The advantage of GaN in such modular designs is
clear when comparing the best-in-class silicon
production designs (100 W), and silicon proto-
types (300 W) which required stacked PCBs and
large heatsinks. Figure 2 shows these silicon
designs plus a new 400 V, 300 W, single-PCB
design using NV6117 GaNFast power ICs which
follows the industry-standard ‘DOSA’ ¼-brick
package and pin-out for simple installation and
upgrade. Over a wide-range 330-425 V input,
DC
and from -40°C to +100°C operating tempera-
ture, the GaN converter delivers the full 300W in
only 30 cc without derating. This means a world’s
best-in-class power density of 10 W/cc, and 2x
more power than any other mass-production DO-
SA-compliant high-voltage ¼-brick converter. The
current 300W design uses an industry-proven,
hard-switched half-bridge topology at a record
MARCH 2021 | www.powerelectronicsnews.com 17