AR 350AH1A, Operating And Service Manual

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Rev B 27
3. THEORY OF OPERATION
3.1 GENERAL
The Model 350AH1A amplifier can be a relatively simple unit to understand. The amplifier is a
straightforward design, with a few control elements in the lineup. The unit’s power supply, control and fault
detection circuits can be easily understood by anyone with a minimal understanding of analog and digital
circuitry.
3.2 AMPLIFIER
Refer to Interconnect Diagram 10036272 and the schematics referred to below.
3.2.1 Amplifier RF Input
From the RF input, the signal path is as follows. From the Type BNC connector on the control panel, the
signal travels to the variable gain amp assembly.
3.2.2 Variable Gain Amp
Refer to Schematic 10043102. The variable gain amplifier is a broadband IC with a voltage-controlled gain
feature. It is powered by ±5VDC.
3.2.3 350W Module
Refer to Schematic 10024788. This module is a Class AB amplifier which uses a driver section and eight
pairs of lateral power MOSFETs as power output devices. Both N channel and P channel devices are used.
The driver circuit is comprised of an operational amplifier stage and a Class AB amplifier stage using two
transistors to obtain the amplitude and power level in order to drive the output devices as a follower circuit.
3.3 POWER SUPPLY
Refer to Schematic Diagram Number 10024922, Interconnect Diagram, 350AH1A . Main power to the unit
is supplied by single phase AC power within the proper range. In series with the line voltage is the 20A Main
circuit breaker CB1, located on the rear panel. This circuit breaker supplies line voltage to the contactor
located just behind the rear panel. The contactor is controlled by the front panel Power ON/Off switch and
interrupted manually by the three-position key-switch labeled Inhibit – Local – Remote . The contactor feeds
AC directly to the primary inputs of the main power supplies. When the main circuit breaker is on, AC power
is fed to the low voltage supply, PS1. Therefore, when the circuit breaker is turned on, the control panel and
basic low-power supplies are alive, and the amplifier is armed for Power On. At this time, the front panel
display is illuminated and the control circuitry is active.
The high-power supply PS2 provides input and output TTL-compatible logic signals for inhibiting the supply
and signaling the control system that the supply is malfunctioning. The fault signal is normally HI, going LO
when a fault is present. The Enable signal must be LO to enable and either HI or Open to inhibit the output.