Assembly Instructions Chapter 4

10-kW UHF Transmitter with Chapter 4, Circuit
Feedforward Drive Descriptions
840A, Rev. 0 4-29
4.2.4 Filament Power Supply
Assembly
The filament power supply assembly
(1299-1107) consists of input terminal
block TB2, status and control terminal
block TB1, the (A1) filament power
supply control board (1293-1304;
Appendix B), and the (A2) programmable
filament power supply (1293-6302).
The 220 VAC is supplied at TB2-1A and
TB2-2A and ground at TB2-3A. There are
three MOVs (VR1 to VR3) mounted on
the terminal block to protect against
voltage spikes and transients. The 220
VAC is fed from TB2-1B, TB2-2B, and
TB2-3B to (A2) the programmable
filament power supply at TB1-L, TB1-N,
and TB1-GND. The output of the power
supply is fed to the filament of (A2-A1)
the diacrode tube.
4.2.4.1 (A1) Filament Power Supply
Control Board (1293-1304; Appendix B)
The filament power supply control board
has five functions:
• Control and status of the three
states of filament voltage (float,
ramp, and operate) for the filament
power supply
• Provide two on-board LEDs for status
indication
• Provide adjustments to the operate
voltage
• Monitor the operate status through
monitoring the +12 VDC supply and
220 VAC power
• Adjust the front panel metering for
the filament voltage and the tube
run-time hour meter control
These functions are controlled through
the software programming in U4, a
Motorola MC68 microcontroller.
Filament Control
When the filament circuit breaker on the
front panel is activated, the filament
control board sets the program control
at J3-1 to achieve an output from the
power supply of 1.5 VDC. The output
from U4 PA0-PA7 controls the DAC U3
voltage output at pin 16, which is
buffered by U5 and sent to J3-1. After
ten minutes of valid power supply
operation, the control board sends a
filament-ready signal at J4-2 out to the
transmitter control board (1137-1003),
allowing the transmitter to be placed in
the Operate mode. Once the Operate
switch has been enabled at the front
panel, the power supply controller
gradually increases the filament
operating voltage. During the ramp-up
phase, every 0.80 seconds the DAC
output at J3-1 to the filament power
supply is increased by one bit. Assuming
no faults, the tube voltage reaches the
operating range three minutes after
closure of the Operate switch. J4-2
(filament OK) is a logic output to the
transmitter control board. Logic 1
indicates that the filament power supply
is at the operate or ramp-down voltage
(-5.0 VDC). Logic 0 indicates that the
power supply is at the float or ramp-up
voltage (- less than 5.0 VDC). During
ramp-down, this logic level is held high
to direct the transmitter control board to
keep the blower operating. The blower
will continue to operate for three
minutes after the float voltage level is
reached.
On-board LED indicators
The on-board visual indication of the
controller state is provided by LED DS1.
This LED is off if the power supply is
disabled; blinking at about 1 Hz if the
float voltage is being held for ten
minutes; blinking at about 2 Hz if the
controller is ready to ramp up the
filament voltage; blinking at 4 Hz if the
controller is ramping the voltage up or
down; and continuously on when the
filament is at operate voltage levels. The