AR 10045879, Operating And Service Manual

Page: 42 / 54

Model 250U1000
24 Rev A
3.2.2 A2 U Series Driver Module (Schematic 10041561)
The 10W driver Module consists of RF matching circuits, an RF transistor, a DC current control circuit, a DC
switching circuit, and a fault detection circuit.
The RF input is fed to a balun transformer (T1). The push-pull output signal of the balun transformer is
connected to the gates of Q1 and Q2. The drains of Q1 and Q2 are connected to a balun transformer (T2). The
RF transistors, Q1 and Q2, have approximately 28 VDC applied to the drains at 1.5A each. The RF stage has
approximately 14 dB of gain and an output compression point of 10W or greater from final amplifiers.
Voltage comparator U1 senses the presence of the –8 VDC. The output of U1 is high if the –8V supply is –5.5
or less. The output of U1 pulls low when the –8 volts is present turning on Mosfet Q3 which supplies the DC
voltages to the drains of Q1 and Q2.
The current through Q1 and Q2 is monitored by U2. The output of U2 is fed to an op amp (U5) which has a
reference voltage on the non-inverting input. It compares the output of U2 to the reference voltage and
generates an error signal to vary the gate voltage of the RF transistors Q1 and Q2 which controls the drain
current.
U3 is a positive 5V regulator. It supplies DC to the current sense circuit, U2, the op amp, U5, and the fault
detection circuit, U6. SW1 is a thermal switch. It closes at a heat sink temperature of approximately 55 o
C to
protect the module in the event of an over-temperature condition.
3.2.3 A3 Four-Way Splitter
The Four-Way Splitter is a broadband splitter. The input signal is split into four equal-amplitude, equal-phase
signals. The amplitude of each signal is approximately 6dB below the input signal when all four outputs are
terminated into 50 Ω loads.
3.2.4 A4 thru A7 U Series Final Module (Schematic 10042997)
The U-Series Final Modules consists of RF matching circuits, an RF transistor (Q1), a bias control circuit, and
a fault detection circuit.
The RF input is fed to a 4:1 balun transformer composed of T1 and T2. The output signal of the 4:1
transformer is connected to the gates of Q1. The drains of Q1 are connected to a 4:1 balun transformer
composed of T3 and T4. Q1 has approximately 28 VDC applied to both drains at a total current of 7A. The
RF stage has approximately 15 dB of gain and an output compression point of 45W or greater.
The current through Q1 is monitored by U2. The output of U2 is fed to an op amp (U3) which has a reference
voltage on the non-inverting input. U3 compares the output of U2 to the reference voltage and generates an
error signal. This error signal varies the gate voltages of Q1 which in turn controls Q1’s current draw.
U7 is a comparator that monitors the output of U2 and generates a fault signal if the drain current varies
outside normal operating conditions. It also monitors the module temperature via a thermistor (R42) and
generates a fault signal in the event of a module over-temperature condition.