AR 10046246, Руководство по эксплуатации и обслуживанию

Страница: 36 / 46

Model 125A250
18 Rev B
3.2.2 A2 100W 400MHz Module Assembly (Schematic 10039874)
The 100W 400MHz Module Assembly 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 34 VDC applied to both drains at a total current of 8.5A. The
RF stage has approximately 21 dB of gain and an output compression point of 90W or greater.
The current through Q1 is monitored by U1. The output of U1 is fed to an op amp (U3) which has a reference
voltage on the non-inverting input. U3 compares the output of U1 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.
U5 is a comparator that monitors the output of U1 and generates a fault signal if the drain current varies
outside normal operating conditions. It also monitors the module temperature via a thermistor (R31) and
generates a fault signal if the module heatsink exceeds approximately 80 o C.
3.3 POWER SUPPLIES (PS1, PS2)
Power supply PS1 supplies a +5VDC housekeeping supply for the control system assemblies A4
Control/Fault Board and A5 Interface Board.
PS1 also su15 VDC at 2.5 amps and -15 VDC at 1 amp. PS1 is a switching supply that automatically
sets the AC input circuits to the correct connections for the line voltage 100-240 VAC input ranges 50/60 Hz.
The +15 VDC at 2.5 amp power supply is fed to the A10 Voltage Regulator board.
The –15 V at 1 amp power supply is fed to the A1 Pre-Amplifier and A2 final module to provide gate voltage
for these modules.
Power Supply PS2 is a single output supply which pr34.0VDC to the RF final stage and to the A10
Voltage Regulator board. Primary AC circuit protection is provided by the circuit breaker in the Power Entry
Module.