This white paper describes the design of power adaptors for systems that distribute power using 400 V DC. The paper particularly considers telecom and data center equipment.

1. Power adapter design for seamless
interface of low voltage DC
equipment to 400V DC distribution
Maurizio Salato, VICOR
BJ Sonnenberg, Dustin J Becker, EMERSON Network Power
David E. Geary, UNIVERSAL Electric Corporation / StarLine DC Solutions

2. Table of content
•
•
•
•
•
Power Adapter Characteristics of Interest
Telco site evolution options
Existing sites transition to 400V DC
Implications of power conversion location
Power Components for 380V Adapter and the
Equalizer concept
• Architectural Matrixes
• System safety and Harmonics considerations
• Conclusions

3. Power Adapter Characteristics of Interest
• Location in the power stream:
–
–
–
–
The power drop box (busway or cable)
The rack power strip
1U space “power shelf” within the rack
Plug‐in unit at “blade” level
• Electrical function and power conversion topologies
• Battery backup “equalization”
• Safety and protections
• Harmonics

4. Telco site evolution options
Today
Next Step
Facility
AC Loads
Utility
Gen
Critical
AC Loads
AC
UPS
Batt
-48V DC
Power
System
AC
-48VDC
Batt
Facility
AC Loads
.
DC
Critical
48V DC
Loads
Facility
DC Loads
AC
DC
Many Transition
Paths Possible
Utility
Gen
●
380V DC
400V DC
Power
System
Batt
Paths forward with 400V DC for larger core sites:
1.
2.
3.
Greenfield with 400V loads (bulk or distributed 400V)
Retrofit/expand -48V loads with 400V main plant (bulk)
Greenfield with bulk 400V to distributed 400V/-48V
Local
Generation
Source
DC DC
Critical
AC Loads
Critical
400V DC
Loads
Critical
-48V DC
Loads

5. Existing sites transition to 400V DC
48V DC bulk equipment
380VDC cabling or bus way
48VDC cabling
380VDC
System
380/48VDC
Conversion
+
Secondary
Distribution
48VDC
Equipment
Rack
380VDC
Equipment
Rack
The main power distribution from a 400V DC system is built with 400V DC bus way or cabling,
directly to 400V DC enabled loads.
For loads requiring 48V DC inputs, a bulk 400V‐48V DC conversion replaces the “secondary
distribution bay” and is located close to the loads to eliminate long 48V DC cable runs.

6. Existing sites transition to 400V DC
48V DC rack mounted equipment
The 400V DC distribution is extended close to the
powered rack .
The options for location of the 400V‐48V DC
conversion depend on the type of feeder used
(bus‐way or cabling) and distribution inside the
rack.
Due to the relatively low power density of 48V DC
powered racks, the conversion section is compact
and can be located in a bus way plug‐in box, a
junction box on top of rack, inside the power strip
itself or in a rack mounted shelf

7. Implications of power conversion location
380V
busway
Adapter
output
supplies
Rack units
management
System
availability /
redundancy
Busway or
wire drop‐box Entire rack
Un‐qualified
operator
(SELV)
Fair
(rack to rack)
Location
Rack
Rack power
shelf
Groups of
units
Un‐qualified
operator
(SELV)
Medium
(group to group)
Individual
unit adapter
Single unit
Qualified
operator
(AC, 400V DC)
Maximum
(unit to unit)

8. Power Components for 380V Adapter
I
SAC
V
32·I
I
V/32
SAC
V
8·I
V/8
K=1/32
K=1/8
BC K=1/32: high voltage bus converter,
260‐400V input, 32:1 ratio, 8‐12.5V output
BC K=1/8: high voltage bus converter,
260‐400V input, 8:1 ratio, 32‐50V output
ZVS BO
ZVS BU
ZVS BB
ZVS BO: Zero Voltage Switching Boost
regulator, 8V min. input, 55V max. output
ZVS BU: Zero Voltage Switching Buck
regulator, 55V max. input, 8V min. output
ZVS BB: Zero Voltage Switching Buck‐Boost
regulator, 32‐55V input, 20‐55V output

9. The Equalizer Concept
•
Compliance to ETSI EN 300 132‐3‐1
•
Regulate ONLY if voltage falls below normal operating range (365 V ± 15 V)
•
96%98% efficiency under normal operating conditions
•
SELV Output

10. 380V to 12V power components matrix
Power distribution
12V Loads
Source
Load
Range
VIN
VOUT
[V]
Regulated
384V ± 1%
380‐388
ETSI EN 300 132‐3‐1
EMERGE >3ms
380V ‐8% +3% 350‐390
380V nom
260‐400
HDD
12V ± 4%
11.5‐12.5
BC K=1/32
BC K=1/8 & BU regulator
Semi‐regulated
12V Backplane
12V ± 2%
11.75‐12.25
BC K=1/32 & BO equalizer
VRMs
12V ± 35%
8‐16

11. 380V to 48V power components matrix
Power distribution
48V Loads
Source
Load
Range
VIN
VOUT
[V]
Regulated
384V ± 1%
48V Backplane
48V ± 2%
47‐49
ETSI 48V
48V nom
36‐60
BC K=1/8
380‐388
BC K=1/8 & BO equalizer
Semi‐regulated
380V ‐8% +3% 350‐390
BC K=1/8 & BB regulator
ETSI EN 300 132‐3‐1
EMERGE >3ms
380V nom
260‐400
BC K=1/8 & BO equalizer
FPA
45V nom
32‐60

12. Adapter power architecture, peak efficiency and
density vs. Distribution Ratio (DR)
Power component density
(components only)
[W/inch3 – (W/cm3)]
Power conversion
peak efficiency
2000 (122)
98%
Non‐equalized output
97%
1200 (73)
96%
Equalized output
95%
Regulated output
94%
400 (25)
Equalizer
Bus Conv.
Bus Conv.
Bus Conv.
Equalizer
+
Power components
+
OR
Regulator
0.8
3
Regulator
Bus Conv.
+
5

13. Safety and Operators protections
The SAC converter galvanically isolates the 400V DC and the low voltage distribution systems
 Isolated, floating supply, 200V max with
respect to hearth.
 Mid‐point resistive grounding early‐detection
system for isolation faults.
 Safely sustains up to 500V operating
input to output voltage differential.
 Low voltage secondary in UL/CSA
60950 qualified SELV range.

14. Harmonics
• AC distribution systems are affected by higher order harmonics
generated by the interaction of AC‐DC converters.
– the impact of high THD on AC distribution systems can affect up to
59% of the installed wiring capacity, leading to significant higher
operating costs or even hazards.
• Bulk power systems and DC‐DC converters generate harmonics that
typically start at the switching frequency of the considered
converter, therefore a much higher frequency than AC‐DC
converters.
– Passive filtering for this type of spectrum is usually effective, small and
avoids low frequency beats that may result from the interaction of
asynchronous DC‐DC converters. Moreover, filter size allows effective
integration within the adapter enclosure.

15. Conclusions
•
•
•
•
400V DC distribution systems offer quantifiable advantages not only for new telecom
and/or datacenter facilities, but also for upgrades of existing ones.
Power component‐based architectures for power adapters have been discussed and
analyzed.
The proposed locations leverage the space available within equipment racks or within
racks’ rows, making maximum use of available space and enabling maximum racks
density as far as equipment loads.
Best location of power adapter for use with legacy loads depends on user preference
based on the following criteria :
–
–
–
–
–
•
Safety
Availability
Efficiency
Ease of harmonics content elimination
Cabling size
For high density loads, the best system architecture from efficiency , reliability and
space savings standpoint is a direct 380VDC connection to the motherboard with on‐
board 380VDC‐48VDC bus converter and direct 48V to processor/memory factorized
power system.