HP 182C - 4-24. Low Voltage Power Supply

Theory
Model 182C
4-19.
An externally applied
signal for
horizontal
deflec-
tion may be connected to
the
EXT
INPUT
jack.
The
EXT
VERNIER controls the externally applied signal and pro-
vides a variable gain adfustment for setting the X-axis dis-
play size. The EXT COUPLING switch provides
for
either
direct
(DC)
or capacitive
(AC)
couplirtg of the external
input signal.
The
external
signal is then
coupled
to a pre-
amplifier,
differentially amplified
by
the output amplifier
and applied to the CRT for horizontal deflection. Position
ing and
horizontal
gain controls
also function
with
external input signals.
4-20.
CIRCUIT DETAILS.
4-21.
INPUT POWER.
4-22.
Input line
power
is supplied by a detachable three
conductor power cord, This cord has a standard plug for
wall outlet connection providing an electrical ground.
Instrument power
input is via a
rear
-panel I EC connector.
Both sides of the line power are filtered immediately at
the power input connector.
4-23.
The line power transformer has two primary
windings. SELECTOR switch
A4S1
connects these wind-
ings in
parallel for
115V operation
and in series for 230V
operation. When set for use with a 11GV source of line
power, fuse A4P
1
protects
against excessive input current.
When operated on 230V line power, fuse
A4E2
is
also
placed in the primary power circuit. With the front panel
LINE toggle switch
A2S1
in the ON position, power is
applied to
the low voltage power supply transformer and
LINE
lampA2DS1 lights.
4-24.
LOW VOLTAGE POWER
SUPPLY.
4-25.
The low voltage supply produces four regulated
voltages for
use
throughout
the
oscilloscope and the plug-
ins:
+
100V, 100V, 415V and -12.6V,
Each
supply is
referenced to the -*-100V supply for regulation purposes,
with the
t-IOOV supply referenced
to a 9-volt
temperature
compensated zener diode A1A2VR2. The -tlOOV and
—100V
supplies
are also
toldback
current
limited,
pro-
viding
short-circuit
protection.
4-26. A simplified block diagram of a typical low voltage
power supply is shown in Figure
4-2.
Unregulated
aliernaiing power Is supplied by the
transformer,
bridge
rectified and filtered. Changes in output voltage caused
by input voltage variation or load changes are detected by
the voltage sensor. Compared against a voltage
reference,
charrges in output voltage are detected and applied as
feed-
back
to the
driver
which controls the scries regulator.
The series regulator
acts as a variable resistance, and
operates to tncrease its series resistance if the
output
voltage is high or decreases resistance
when the output
voltage is low. The action of the series
regulator is to
maintain
output voltage
at
a constant level.
4-27.
Current sensing takes place simultaneously with
voltage sensing. If the load current increases
above a
pre-set level, the current
sensor detects the increased
voltage drop across the series resistor. This increased
voltage causes the driver
to bias the series regulator off.
4-28. +100-VOLT SUPPLY. The
+100V supply is
used
throughout the LVP5 as a
reference for
the other supplies.
It
is
both voltage and current regulated.
Refer
to the LVPS
schematic while reading the
following
explanation.
LOAD
Figure
4-2. Simplified Low
Voltage Power
Supply