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Model 721A
Sect. I Page 1
SECTION I
GENERAL INFORMATION
1-1
MANUAL CONTENT
The material for this instruction manual is written
in five sections:
Section I contains material of a general nature.
Section II explains how to operate the power supply.
Section
III explains
how
the circuit operates.
Section IV covers maintenance and trouble shooting
procedures.
Section V is a table of replaceable parts.
1-2
GENERAL DESCRIPTION
The
Model 721A Power Supply produces a dc
regulated voltage adjustable from 0 to 30 volts.
The supply makes load circuit performance inde¬
pendent of external power supply influences. The
supply has very low source impedance and ex¬
cellent regulation against change in line and/or load.
This supply is especially useful as a source of
power for transistor circuits. A circuit is provided
which electronically limits the maximum output cur¬
rent that can be supplied to four nominal values
selected by a front panel switch. This feature helps
prevent the accidental destruction of an expensive
transistor should an accident occur that would nor¬
mally allow excessive current to flow through it.
The SHORT CIRCUIT CURRENT switch can be set
to the value which is closest above the normal
operating current.
The supply will automatically
limit the peak current flow to this nominal value
regardless of the load resistance.
Built-In Metering
A built-in meter allows either output voltage or
current to be monitored as selected by the METER
RANGE switch.
Isolated Output
The power supply has both output terminals in¬
sulated from chassis ground. Either terminal may
be grounded or a number of supplies may be con¬
nected in series to obtain higher voltages. Insula¬
tion is such that the supply may be operated as
high as 400 volts off of ground.
Parallel Operation
Parallel operation of two or more supplies is pos¬
sible due to the unique electronic current limiting
switch.
The supplies will each contribute only the
number of milliamperes selected by the SHORT
CIRCUIT CURRENT switch. The individual supplies
may be loaded to approximately 225 ma with some
reduction in ripple and regulation characteristics.
Reliability
The Model 72XA Power Supply is very compact, and
has low internal losses, which are made possible
by fully transistorized circuitry. The trouble free
characteristics of transistors together with the use
of high quality components throughout, will result
in a minimum of maintenance.
1-3
INSPECTION
When the Model 721A is received, inspect it for
damage received in transit. Operate the instrument
to make certain that it is functioning satisfactorily.
If damage is evident, follow the procedures outlined
in the "CLAIM FOR DAMAGE IN SHIPMENT"
page of this manual.
1-4
POWER CABLE
The power cable consists of three conductors and
is terminated in a three-prong male connector rec¬
ommended by the National Electrical Manufac-
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