Power
4-4 Issue 8.0 July 2002
The two independent −48 volt office power feeders (A and B) enter each shelf via
a power interface circuit and are distributed to the circuit packs (Figure 4-3) via
the printed backplane. The power interface circuit consists of a green PWR ON
LED, two power filter assemblies, and two radio-frequency (RF) filters.
The green PWR ON LED (located on the user panel and filter panel) shows that
the shelf is receiving fused −48 volt power. The green PWR ON LED will remain
lighted as long as either −48 volt power feeder is supplying power to the shelf.
Each power filter assembly smooths the input current and reduces the converter
switching noise to the allowed limit. Each power feeder also passes through an RF
filter at the interconnection panel to remove any RF energy before going to the
backplane.
From the RF filters, the power feeders are connected to the backplane and
distributed to the circuit packs on the shelf. Each backplane power feeder
connects to the circuit pack via four backplane pins. One pin is longer than the
other three power pins and connects to the circuit pack first. This long pin feeds a
surge resistor to limit in-rush currents and prevents voltage dropouts on the power
feeders.
Figure 4-3. Shelf Power Distribution
A
B
Power Distribution and Fuse Panel
Feeder B
and
Return
and
Return
Feeder A
Power
Filter
Assembly
Power
Filter
Assembly
Power
Interface
Circuit
Shelf
EMC Enclosure
Backplane
Circuit
Pack
Circuit
Pack
Circuit
Pack
Circuit
Pack
Circuit
Pack
Return
Return
RF
Filters
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