Overcurrent Protection; Undervoltage Protection; Power Failures - HP 3000 III Series Manual

HP 3242lA Series III Power Supplies
15 to 100 amperes. It augments the approximate 55-ampere, 5-volt
output of the HP 1303l0A Power Supply which powers the CPU/lOP, the
HP 303llA Power Supply, and portions of the computer I/O area.
Figure 9-5 illustrates the major functional areas of the HP
303l2A Power Supply, Interface Board, part no. 303l2-600
J
02. The
model 62605M Power Supply is also shown to illustrate the rela-
tionship 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 303l0A Power Supply sys-
tem 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 sup-
ply provides the operating potentials for the circuits including
the reference voltage (adjusted to 4.75 volts by potentiometer
R52) used by several functional circuits on the interface board.
9-34. Overcurrent Protection
The operating current configura tor monitors the +5V load on the
62605M Power Supply and is activated whenever the load increases
10 amperes above the normal load. When switch S2 is pressed, ADJ
potentiometer R32 is adjusted at the normal steady state current
level. When S2 is released, the threshold is automatically in-
cremented to sense a current 10 amperes above the nominal value
se t with R32. Tr ans ie nt ove rcur re nts exce ed ing 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 se ts the la tch (caus ing the
overcurrent indicator to light continually) and shuts down the
62605M Power Supply output by pulling the Al terminal control
voltage below its turn on value. The Cal/Test switch Sl and Cal
Adj potentiometer R26 are used at the factory to calibrate the
operating current configurator to the resistance of the high cur-
rent wires connected to the power supply. These controls are
normally not used in the field and should be left as they are.
9-35. Undervoltage Protection
The undervoltage detector, connected to the +S (+sense) terminal
of the power supply, sets the Power Supply Up (PSU) signal low
(IV) to the system whenever the output voltage at the load drops
below 4.6lV. The PSU signal is restored to the open circuit con-
dition whenever the output voltage at the load rises above 4.8lV.
9-36. Power Failures
An ac power failure sensed by the HP 30310A Power Supply causes a
Power Fail Warning (PFW) signal to be sent to the
cpu.
There-
fore, the HP 303l2A does not require a power failure de tector.
Maximum utilization of this detection capability can only be ob-
tained when the
HP
30310A and
HP 303l2A are supplied
from the
same ac power source.
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