HP Lab Series User Manual

SECTION IV
PRINCIPLES OF OPERATION
..
REFERENCE
REFERENCE
-
CIRCUIT
VOLTAGES
CONSTAN.T
-
T
CURRENT
-
BIAS
BIAS
,...
INPUT .
-
SUPPLY
~
VOLTAGES
CIRCUIT . I+
AC
POWER
I
XFMR
RECTIFIER,
SERIES
+
-
FILTER,
..
REG.
-
PREREG.
CURRENT
SAMPLING
RESISTOR
-
/\IVER
-
.. ~-
OR 'ii
CONSTANT
.., GATE
-
DC
4-
VOLTAGE
INPUT
OUTPUT
ERROR
----
-
CIRCUIT
AllPL.
-
r..-
PRE REG.
-
CONTROL
CIRCUIT
....
I
f
METER
•
CIRCUIT
,
,,
-
NOTE•
-
----- DENOTES VOL TA6E FEEDBACK PATH
----- DENOTES CURRENT FEEDBACK PATH
Figure 4-1. Overall Block Diagram
4-1 OVERALL BLOCK DIAGRAM DISCUSSION
4-2 The major circuits of the power supply are
shown on the overall block diagram of Figure 4-1.
The ac input voltage is first rectified and applied
to the preregulator SCR which operates in conjunc-
tion with the SCR control circuit to fonn a feedback
loop. This· preregulator feedback loop minimizes
the power dissipated by the series re.gulator by
keeping the voltage drop across the regulator at a
low and constant level.
4-3 To accomplish this, the SCR control circuit
issues a phase adjusted firing pulse to the SCR
once during each half cycle of the input ac. The
control circuit continuously samples the output
voltage, the input line voltage (from T3), and the
voltage across the series regulator and, on the
basis of these inputs, determines at what time
each fll:ing pulse is generated.
4-1
4 ... 4 The phase adjusted output of the SCR is ap-
plied to the series regulator which varies its con-
duction to provide a regulated voltage or current at
the output terminals.
4-5 The series regulator is part of another feed-
back loop which consists of the error and driver
amplifiers and the Constant Voltage/Constant Cur-
rent comparators. The series regulator feedback
loop provides fine and "fast" regulation of the out-
put while the preregulator feedback loop handles
large, relatively slow, regulation demands. ·
4-6 The feedback signals that control the conduc-
tion of the series regulator are originated within the
constant voltage or constant current comparator.
During constant voltage operation the constant volt-
age comparator continuously compares the output
voltage of the supply with the drop across the VOLT-
AGE controls. If these voltages are not equal, the
•
•
•

HP Lab Series Specifications

General

Brand	HP
Model	Lab Series
Category	Power Supply
Language	English