Power Supplies - HP 8340B Manual

The remaining bands (7.0
GHz
to the maximum output frequency) are generated by multiplying the YO
frequency
in the SYTM.
A
step recovery diode (SRD)
in
the SYTM, when biased
properly, generates
harmonics of the
input signal. A
YIG-tuned
filter tracks the desired harmonic, allowing
it
to pass
through to the high band coupler and step attenuator to the RF output. The SYTM driver
provides the
necessary circuitry
for the YIG-tuned
filter in the
SYTM
to properly track the YO. Leveling in these
bands
is
the same as in
band
1.
Pulse modulation
is produced by the pulse modulator driver and
two
fast response time pulse modu¬
lators.
The
low band pulse modulator, located just before the low band mixer,
is
used
when
the
instrument operates below 2.3 GHz. Operation above 2.3
GHz
uses the high band pulse modulator
inside the mod/splitter.
ALC modulation
(fixed power,
AM,
etc.) is produced
by
the
ALC modulator driver
and the
ALC
modu¬
lators. The low band modulator
is
located in the 3.7 GHz
oscillator;
the high band modulator
is
located
in the mod/splitter.
POWER SUPPLIES
The power supply produces eight regulated voltage
levels,
four positive supplies and four negative
supplies:
• +22, +20, +12, +5.2,
-5.2, -10, -15,
and
-40V
The
+22
volt
supply powers
the 10
MHz
reference oscillator heater
coil.
This is the only supply that
actually
produces an output
when the instrument is
switched to
STANDBY.
All
supplies except for the +
22 volt supply are referenced either directly or indirectly to the +20
volt
supply.
In
STANDBY
mode, the
+20
volt supply shuts
down. This
in turn shuts down the regulators
for
all
other supplies (except the
+22
volt supply).
NOTE: Although these supplies are shut down,
line
power
is still
on, the
line
module, transformer,
motherboard, rectifiers, and filter
caps
still
have
full
voltage potentials on them. Therefore, hazardous
voltages exist
in
these
sections of the instrument even when the front panel power
switch is set to
standby.
The
+20,
—15, -10,
and —40V supplies deliver current to the low noise analog circuits and the
microcircuits.
The
+12, +5.2,
—5.2, and —15V supplies deliver power to the
digital and noncritical
analog
circuits. Over-temperature protection, current limit, and over-voltage protection are built into
each supply.
The
output voltage
of
each supply (excluding the +22V
supply) is
monitored.
If
any of
these supplies drop out of regulation, the instrument microprocessor is
flagged.
HP 8340B/41B
Assembly-Level Service Overall Instrument Theory A-7/A-8