Operations Manual

RF Technology R50 Page 17
5 CIRCUIT DESCRIPTION
5.7 Power Generator Section (Sheet 7)
U609B, U607A and U607B are working as a flat/de-emphasis response switch, it can
be selected by control signal FLAT and DE_EMPHA from the MicroController U204.
U607D and U607C is the squelch switch for line output and speaker.
U609C is the amplifies for 600W line output, U609D is the amplifier for direct audio
output, the output level of 600W line an direct audio are adjustable via VR601 on the
front panel.
U604 is the power amplifier for internal and external speaker, the power level can be
adjusted by VR602 on the front panel.
Depending on the squelch, RL602 will apply a 12VDC to the 600W line output when
loop function is selected. If the loop function is not used, RL602 always stay in the
position of which C619 is bypassed. The position of RL602 is controlled by the signal
LOOP/VOLTS_SEL from the MicroController U204.
Opto-coupled transistor Switch U601 provides a COS (Carrier Operated Switch)
output which is controlled by COS_POLARITY signal from the MicroController. The
output COS+ and COS- can be used as +12V DC source or a free switch depending on
the status of the relay RL601, RL601 is controlled by COS_VOLTS_ON/OFF signal
from the MicroController U204.
Discriminated audio level is detected by D604 and C623, signal LINE_LEVEL is
connected to the analog-digital converter input pin of the MicroController for
calibration purpose.
5.7 Power Generation Section (Sheet 7)
There are three switch-mode dc-dc converters in the board. These use monolithic
converters based on the National LM2595. Two of the converters are 12V converters
and one is a 5V converter.
The power in to the whole exciter is the voltage rail 28V.
U907 converts this down to 12V.
U908 is set up as an inverter, and uses the 12V rail to create -12V.
U909 converts the +12V rail to +5V for all the digital circuitry.
The +12V rail is used to power the two on-board relays, as well as up to one extra off-
board relay. It is also dropped, via a linear regulator (U910) to produce the +10V rail,
which in turn is dropped by another linear regulator U911 to produce +5Q.
Similarly U913 and U914 are linear regulators that produce -10V and -5V from the -
12V output of U908.
+2.5Vand -2.5V are not used in the R50 receiver, the reason of being showed on the
schematic diagram is to keep same design of the T50 power generation section.