The document describes different power distribution architectures for server and networking equipment. It proposes a Controlled Bus Architecture where the backplane voltage is held constant, allowing bus converters to operate at higher efficiency with a narrow input voltage range. This approach offers higher distribution and converter efficiency, easier interfacing of power sources, and increased board density compared to an unregulated Intermediate Bus Architecture with a wide voltage range. The cost is an additional regulation stage for backup power systems.

1. Controlled Bus Architecture
As an alternate to the Intermediate Bus Architecture
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2. Definition of Controlled Bus Architecture
› By setting the backplane voltage to a constant that does not
vary under any condition, the downstream power distribution
and bus converters operate at higher efficiency.
› Enabling bus converters to be optimized for the narrow input
voltage, providing the opportunity
for further efficiency increase
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3. Benefits of the Control Bus Architecture
› CBA brings the following benefits to the system
– Higher distribution efficiency
– Higher bus converter efficiency
– Bus converters optimized for narrow input voltage range
– Multiple sources can be effectively interfaced
– Router or server mainboard density effectively increased
› At the following cost
– Regulation stage for DC backup system, which operate only
when necessary
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4. Unregulated IBA, Wide Range IBC
Rack / Facility Backplane Switch Card or Server, Router Mainboard
DC backup
36-54V Wide range 6.5-11V
IBC 5:1
85- Power Entry
265V Module (PEM) ¼ Brick
AC AC/DC Max Power: 600W
Isolation
FUNCTION: ORing Distribution Distribution
Transformation
On a system perspective, existing systems operate majority of the time 43.6Wa regulated
Maximum power dissipation: 1.4W 13.9W
with
backplane, when main energy is sourced through PEM (power entry module). The need for
typical backplane voltage range arises if various batteries’ (or fuel cells, or equivalent)
configurations are used as backup, simply interfaced through an OR-ing device. So, by adding
a simple regulating stage just to the backup block, the need for wide input voltage range is
avoided altogether.
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5. Controlled Bus, Boost Regulator
Rack / Facility Backplane Switch Card or Server, Router Mainboard
36-54V
Boost
DC backup
54V Narrow range 11V
IBC 5:1
85- Power Entry
265V Module (PEM) ¼ Brick
AC AC/DC Max Power: 900W
Isolation
FUNCTION: Equalization Distribution Distribution
Transformation
Maximum Power Dissipation: 12.6W 6.2W 16.9W
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6. Controlled Bus, Buck-Boost Regulator
Rack / Facility Backplane Switch Card or Server, Router Mainboard
36-72V
Buck-boost
DC backup
54V Narrow range 11V
IBC 5:1
85- Power Entry
265V Module (PEM) ¼ Brick
AC AC/DC Max Power: 900W
Isolation
FUNCTION: Equalization Distribution Distribution
Transformation
Maximum Power Dissipation: 15.8W 6.2W 16.9W
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7. Controlled Bus, DC-DC Converter
Rack / Facility Backplane Switch Card or Server, Router Mainboard
36-72V DC/DC
DC backup
+
-
36-72V DC/DC 54V 11V
DC source
Narrow range
IBC 5:1
85- Power Entry
265V Module (PEM) ¼ Brick
AC AC/DC Max Power: 900W
Isolation Isolation
FUNCTION: Distribution Distribution
Equalization Transformation
Maximum Power Dissipation: 32.5W 6.2W 16.9W
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8. Test Case
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9. Assumptions this test case
› Load power: 600 W
› Backplane total interconnect resistance: 50 mW
› Intermediate Bus total distribution resistance: 1.9 mW
› OR-ing resistance: 5 mW
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10. Unregulated IBA, Wide-Range IBC
Rack / Facility Backplane Switch Card or Server, Router Mainboard
DC backup
36-54V Wide range 6.5-11V
IBC 5:1
85- Power Entry
265V Module (PEM) ¼ Brick
AC AC/DC Max Power: 600W
Isolation
FUNCTION: ORing Distribution Distribution
Transformation
Maximum power dissipation: 1.4W 13.9W 43.6W
Source Source Voltage OR-ing losses Backplane losses IBC losses Distribution losses Load current Total efficiency Losses on board
V % W % W % W % W A % W
PEM 54 n/a 0.0 99.0% 6.2 98.0% 12.2 99.0% 5.9 55.6 96.0% 18.2
DC 36 99.8% 1.4 97.7% 13.9 95.2% 30.3 97.8% 13.4 83.3 90.8% 43.6
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11. Controlled Bus, Boost Regulator
Rack / Facility Backplane Switch Card or Server, Router Mainboard
36-54V
Boost
DC backup
54V Narrow range 11V
IBC 5:1
85- Power Entry
265V Module (PEM) ¼ Brick
AC AC/DC Max Power: 900W
Isolation
FUNCTION: Equalization Distribution Distribution
Transformation
Maximum Power Dissipation: 12.6W 6.2W 16.9W
Source Source Voltage Boost losses Backplane losses IBC losses Distribution losses Load current Total efficiency Losses on board
V % W % W % W % W A % W
PEM 54 n/a 0.0 99.0% 6.2 98.2% 11.0 99.0% 5.9 55.6 96.2% 16.9
DC 36 98.0% 12.6 99.0% 6.2 98.2% 11.0 99.0% 5.9 55.6 94.3% 16.9
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12. Controlled Bus, Buck-Boost Regulator
Rack / Facility Backplane Switch Card or Server, Router Mainboard
36-72V
Buck-boost
DC backup
54V Narrow range 11V
IBC 5:1
85- Power Entry
265V Module (PEM) ¼ Brick
AC AC/DC Max Power: 900W
Isolation
FUNCTION: Equalization Distribution Distribution
Transformation
Maximum Power Dissipation: 15.8W 6.2W 16.9W
Source Source Voltage Buck-boost losses Backplane losses IBC losses Distribution losses Load current Total efficiency Losses on board
V % W % W % W % W A % W
PEM 54 n/a 0.0 99.0% 6.2 98.2% 11.0 99.0% 5.9 55.6 96.2% 16.9
DC 36 97.5% 15.8 99.0% 6.2 98.2% 11.0 99.0% 5.9 55.6 93.8% 16.9
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13. Controlled Bus, DC-DC Converter
Rack / Facility Backplane Switch Card or Server, Router Mainboard
36-72V DC/DC
DC backup
+
-
36-72V DC/DC 54V 11V
DC source
Narrow range
IBC 5:1
85- Power Entry
265V Module (PEM) ¼ Brick
AC AC/DC Max Power: 900W
Isolation Isolation
FUNCTION: Distribution Distribution
Equalization Transformation
Maximum Power Dissipation: 32.5W 6.2W 16.9W
Source Source Voltage DC/DC losses Backplane losses IBC losses Distribution losses Load current Total efficiency Losses on board
V % W % W % W % W A % W
PEM 54 n/a 0.0 99.0% 6.2 98.2% 11.0 99.0% 5.9 55.6 96.2% 16.9
DC 36 95.0% 32.5 99.0% 6.2 98.2% 11.0 99.0% 5.9 55.6 91.4% 16.9
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14. Conclusions
› A Controlled Bus Architecture enables:
– 61% reduction in worst case intermediate bus conversion and distribution
losses on server / router board
– As much as 3.5% efficiency improvement under worst case input voltage
(36 Vdc)
– 50% increase in IBC power density (900 W QB)
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