CHPA
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ERIES
D
OC
.01023245
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1-7
1.4.4 Power
Processor
Module
The power processor circuits provide the necessary line and load regulation of the input 375
VDC bus, which is converted via the switch regulator and bridge circuit to a nominal 230 VAC,
25 kHz to drive the high-voltage module. A sample of the helix high-voltage output is returned
to the switch regulator for error feedback correction and sends a pulse-width modulated signal
through an optical isolator to the switching transistors. This approach allows careful regulation
of the TWT helix and collector voltages protecting both supplies from
overvoltage/undervoltage or short-circuit conditions. Low-voltage outputs produced by the
power processor (+/-15 VDC, +5VDC, and 16 VAC) are used to operate various internal circuit
functions. In addition, power for the RF monitor circuit, front panel display, SSIPA, and
optional linearizer. Internal sensors provide the necessary over-current protection functions.
1.4.5 High-Voltage
Module
The High-Voltage Module provides the following key power supply functions: regulated TWT
heater supply, regulated TWT high-voltage helix and collector supplies, helix supply
current/voltage monitoring, and fault protection.
The High-Voltage Module contains the transformers, rectifiers, filters, and voltage/current
sense circuits for all critical TWT voltages and currents. The incoming 230 VAC, 25 kHz signal
is applied to the primary of a multi-section high-voltage transformer, which provides all of the
high-voltage levels necessary to operate the traveling wave tube. Since the helix and collectors
share the same transformer and regulator, the high-voltage circuit design establishes the
collector voltages at 52 percent (collector #1) and 26 percent (collector #2) depression below the
helix voltage. This relationship permits optimum efficiency and substantial energy savings
while extending the useful life of the TWT. A separate step-down transformer with rectifier and
filter network operating off the 16 VAC supply is employed to provide the regulated low
voltage to power the TWT heater.
1.4.6
RF Power Monitor Module
The RF power monitor assembly receives signals from the reflected and forward power RF
detectors for use in fault/alarm sensing and power metering. This monitor assembly feeds
voltages to the microprocessor controller; it is the controller that monitors the RF levels to
determine RF high/low faults or high/low alarms. This assembly also contains hardware for
peak measurements. The reflected RF fault sensor protects the TWT against excessive reflected
power due to abnormal waveguide or antenna conditions.
1.4.7
Control and Display Modules
The Control and Display modules are designed to assure correct operation of the power
amplifier with minimal operator training. These microprocessor-based modules provide
automatic sequencing of CHPA operation and monitoring and control of all critical parameters
via both the front and rear panel interfaces. Flash RAM allows firmware updates to be made
without opening the unit.
