AT&T 3B2/300 Technical Reference Manual page 570

- - - - - - - - - - - - - - - - - - - - - - - - - - - FUNCTIONAL DESCRIPTION
AT&T Expansion Module Power Supply
Figure 3-104 is a functional block diagram of an AT&T/XM Power Supply and Figure 3-105 is a
functional block diagram of an AT&T XM/405S/900S Power Supply. Color codes and power
connector pin identification for the power cables are shown in these figures. The equipment mounted
in the AT&T/XM requires +5 volt (VCC) and +12 volt power. The power supply upper trip point for
VCC is between +6.00 volt and +6.75 volt. The various drives (hard disk, floppy, and cartridge tape)
require +5 volt and + 12 volt.
The commercial AC line is fused and filtered at the Power Supply Set input. The input AC line
voltage is selected for either 115 volt AC or 220 to 240 volt AC operation. The Voltage Select Jumper is
a factory installed jumper. Different solution packages are provided to support the different input AC
lines.
Cooling for the power supply and the equipment mounted in the AT&T/XM cabinet is provided by
a current load sensitive fan in the power supply assembly. As additional equipment is added to the
configuration, the fan speed increases in response to the increased load. Unfiltered air is pulled from
the front and left side of the cabinet and is exhausted at the back of the power supply.
FUNCTIONAL DESCRIPTION 3-317