Broadcast Electronics AM-2.5E, Руководство пользователя

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4-24
4-123. The fault detection circuit: 1) processes lightning and over-temperature signals and
2) analyzes forward and reflected power signals. As determined by the the fault
condition, the fault detection circuit will generate a fast or slow control signal to the
up/down counter circuit. The counter circuit will respond by decreasing the power control
voltage at digital-to-analog converter U42. U42 will respond by decreasing the output
power to an acceptable level. Once the condition which caused the fault to occur is
removed, the fault detection circuitry will automatically output a control signal to
increase power to a normal level.
4-124. Forward/Reflected Power Circuitry. Samples of the transmitter forward and reflected
power are processed by forward and reflected power circuits on the controller circuit
board. Forward power samples from the directional coupler circuit board are applied to
the forward power circuit. The forward power circuit converts the sample into a dc signal
for application to the fault detection circuitry and to the meter switch circuit board.
Reflected power samples from the directional coupler circuit board are applied to the
reflected power circuit. The reflected power circuit converts the sample into a dc signal
for application to the fault detection circuit and the meter switch circuit board.
4-125. Meter Switch Circuit Board. Forward and Reflected power samples from the controller
circuit board are applied to the meter switch circuit board. The circuit board allows the
selection of forward power, reflected power, and ac input samples for display on forward
power meter M1 and reflected power meter M2.
4-126. RF Output Power Control - Power Supply Circuit Board/RF Power Modules. The power
control PWM signal from the controller circuit board is applied to a correction circuit on
the power supply circuit board. The PWM signal is converted to a dc signal and combined
with a dc feedback signal to generate a power control signal for application to the switch
regulator power control PWM circuit. The circuit converts the dc signal into two PWM
180 degree out-of-phase square-wave drive signals. The square-wave drive signals are
applied to a driver circuit. The driver circuit outputs the out-of-phase square-wave
signals to an IGBT transistor regulator circuit. The regulator circuit transistors are
operated to on for a specific time duration to generate a specific B- supply voltage. The
B- supply voltage is filtered by capacitor C55 and applied to the forward power converter
on the modulator circuit boards.
4-127. The main operating supply B+ leg is created by a SCR controlled bridge rectifier circuit.
AC power from an ac input filter is applied to the SCR controlled bridge rectifier. The
rectifier is controlled by a soft-start circuit. The full-wave rectified dc potential is filtered
by capacitors C24 through C27. The output of the filter generates the positive leg of a B
supply. The B+ line of the power supply is applied to the forward power converter circuit
on modulator circuit boards and the RF amplifier transistors on RF amplifier circuit
boards.
4-128. To provide an example of output power control operation, a 10 kW output level is required
from the transmitter. The controller power control PWM duty-cycle will be
approximately 85%. The power supply will respond by generating a 120 volt B- supply
for application to the forward power converter on the modulator circuit boards. The
modulator circuit boards will output a dc voltage which varies at an audio rate to the
amplifier circuit boards. The amplifier circuit boards will respond by using the modulator
circuit board dc voltage and the B+ leg of the main supply to amplify the RF drive signal
from the exciter circuit board.