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Model 722A
SECTION IV
PRINCIPLES OF OPERATION
Section IV
Paragraphs 4-1 to 4-4
"
4-1. OVERALL BLOCK DIAGRAM.
4-2. Referring to figure 4-2, block diagram, note
that the power-line voltage passes through a power
transformer, a variable transformer, and then to a
bridge rectifier circuit.
The COARSE VOLTAGE
control varies the voltage from the variable voltage
transformer delivered to the bridge rectifier.
The
rectified ac from the rectifier is filtered and supplied
to the series regulator.
The current goes through
the series regulator to the load. A voltmeter across
the output and an ammeter in series with the output
monitors the direct voltage and current fed to the load.
Current and voltage sampling circuits feed the current
limiter.
The current limiter enables the operator to
set the maximum current the Model 722A will deliver
to the load to any value between 0.1 amp and 2.0 amps.
The current limiter also serves to limit the maxi-
mum power dissipated in the series regulator to a
safe value.
The amplified dc voltage change at the
output is applied as a voltage to the series regulators
which tends to counteract the change in output voltage.
The reference power supply furnishes constant volt-
ages which are used throughout the instrument for
reference and supply purposes. Terminals are pro-
vided for remote sensing so the sensing voltage can
be connected to the output externally.
Note
In discussions that follow, the positive side
of the output voltage is considered circllit
ground.
4-3. RECTIFYING AND FILTERING CIRCUITS.
4-4. Referring to figure 4-1 note that alternating cur-
rent is fed through a conventional power transformer
Tl into a variable autotransformer T2. The purpose
of T2 is to keep the voltage across the series regu-
lators Q1 and Q2 more or less constant regardless
of the output voltage. Transformer T2 is ganged with
the output voltage control (COARSE VOLTAGE) R25.
If the output voltage were reduced to a low value with-
out reducing the input voltage to the voltage regulator,
excessive power would have to be dissipated in the
transistors of the series regulator at maximum output
current.
By the use of a variable autotransformer·
this dissipation is kept to acceptable values.
TI
POWER
TRANS-
FORMER
T2
VARIABLE
TRANSFORMER
VOLTAGE
SAMPLING
POINT")
SERIES
REGULATOR
CURRENT
SAMPLING
POINT)
RIB
AC
IN
CURRENT-
POWER
LIMITER
OUTPUT
j
L . . . - - - - - - - - - + - - - - - - - - - - - - - - - _.........
--+--0+
01155-1
REFERENCE
SUPPLY
Figure 4-2. Block Diagram
BD-L-Z47B
LOCAL
I
iL-
l
f
L...-_;'-'
OREMOTE
SENSING
REMOTEU.
4-1
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