AT&T 3B2/300 Technical Reference Manual page 563

FUNCTIONAL D E S C R I P T I O N - - - - - - - - - - - - - - - - - - - - - - - - - - -
Version 3 382 Computer Power
Figures 3-100 and 3-101 are functional block diagrams of the 3B2/500 computer Power Supply and
the 3B2/600 and 700 computers Power Supply. Figure 3-102 is a functional block diagram of a power
supply for a 3B2 computer with embedded SCSI.
Color codes and power connector pin identification for the power cables are shown in the figures.
The 3B2 computer requires +5 volt (VCC), +12 volt, and -12 volt power. Logic power is +5 volt. The
power supply upper trip point for VCC is between +5.5 volt and +7.0 volt. The Dual Universal
Asynchronous Receiver/Transmitter (DUART) uses +12 volt and -12 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 automatically set for either 115 volt AC or 220 to 240 volt AC operation.
Cooling for the power supply and the 3B2 computer 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.
3-310 TECHNICAL REFERENCE MANUAL