HP 3000 SERIES II System Service Manual page 200

HP 30312A Power Supply
8-55. HP 30312A POWER SUPPLY
The HP 30312A Power Supply delivers up to 100 amperes of five-volt power for operation of the
interface PCAs in the I/O area of the' computer. The power supply is an HP 62605M Power Supply
modified by adding· a power switch, fuse, AC receptacle, and a threshold adjustment circuit. The
threshold adjustment circuit is adjusted when the system is configured to provide overcurrent
shutdown of the HP 62605M Power Supply when the drain on the power supply exceeds a
predetermined amount by ten amperes.
The information to follow covers only the items and circuit added to the HP 62605M Power
Supply. The HP 62605M Power Supply is described in Modular Power Supplies, Land M Series,
Models. 62605L, 62605M, and 62615M, manual (part number 5950-1756). The Model 62605M is
equipped with OptIon 106 which enables the power supply to operate on 187 to 250 volts AC input
power.
The HP 30312A Power Supply provides .five-volt power over a current range nominally 15 to 100
amperes. It augments the approximate 55-ampere, five-volt output of the HP 30310A Power Supply
which powers the CPU/lOP, the HP 30311A Power Supply, and portions of the computer I/O area.
B-56. THEORY OF OPERATION
The following paragraphs contain the theory of operation for the HP 30312A Power Supply
Interface Board (part number 30312-60002). Principles of operation for the model 62605M Power
Supply are contained in its associated Operating and Service Manual, HP part number 5950-1756.
Figure B-8 is a simplified block diagram of the HP 30312A Power Supply showing the major
functional areas of the interface board. The model 62605M Power Supply is also shown to illustrate
the relationship between the power supply and the interface board. The interface logic is required
to properly sense and control the 62605M Power Supply with the existing HP 30310A Power
Supply system DC control lines (DCE and PSU). Input power of 208/230 VAC is applied to the
power supply and interface board by POWER switch S3 through the eight-ampere fuse.· An internal
power supply provides the operating potentials for the circuits
~ncluding
the reference voltage
(adjusted to 4.75 volts by potentiometer R51) used by several functional circuits on the interface
board.
B-57. OVERCURRENT PROTECTION. The operating current configurator monitors the +5 volt
load on the 62605M Power Supply and is activated whenever the load increases 10 amperes above
the normal load. When S2 is pressed, ADJ potentiometer R32 is adjusted at the normal steady state
current level. When S2 is released, the threshold is automatically incremented to sense a current 10
amperes above'the nominal value set with R32.
Transient overcurrents exceeding the 10-ampere margin cause the over current indicator (located
above switch S2) to light for the transient time interval. The two-second timer prevents the power
supply from shutting down when overloads are less than two seconds long. When such overloads last
longer than two seconds, the two-second timer sets the latch (causing the over current indicator to
light continually) and shuts down the 62605M Power Supply output by pulling the Al terminal
control voltage below its turnon value.
JAN 1977
B-39