Codan NGT 2010 RF Technical & Service Manual page 544

High power—Technical description
Power Supply PCB
Drawing
The Power Supply PCB is a switchmode DC–DC converter with two separate channels,
one for each amplifier stage. Each subconverter uses a LM3524 switchmode power
controller part, one acting as the master controller (IC1), the other as the slave (IC101).
The outputs from the master and slave are fed to the respective gates of the output drive
FETs (V5 and V105) via a gate drive part (IC2 and IC102).
The output voltage is limited to a minimum voltage of approximately 33 V DC under no
load, and can be increased to 50 V DC if required, depending on the minimum voltage
swing of the amplifier output transistors. The output current is sensed by the output
current mirror circuit (IC3 and IC103), which measures the current across a 5 mΩ
resistor in the output path. A power limit is achieved by modifying the measured current
with a sample of the output voltage, so the current limit becomes inversely proportional
to the output voltage.
This process ensures the output voltage is the minimum voltage required by the
amplifiers for the operating conditions, while still meeting specification and providing
the best possible amplifier efficiency. This has the effect of minimising raw power
supply requirements, and heating the amplifier.
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NGT Transceiver System Technical Service Manual