Operating instructions

RF Technology R50 Page 13
closes depends on the way in which the channel is programmed by the user.
The position of RL602 is controlled by the signal LOOP/VOLTS_SEL from
the MicroController.
Opto-coupled transistor switch U601 provides a COS (Carrier Operated Switch)
output which is controlled by the digital 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 the digital COS_VOLTS_ON/OFF signal from the
MicroController.
5.7 Power Generation Section (Sheet 7)
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, which, in turn, is dropped by a further linear regulator (U912) to
produce +2.5V.
Similarly U913, U914, and U915 are linear regulators that produce –10V, -5V, and –
2.5V from the –12V output of U908.
+10, +5Q, and +2.5V, -10V, -5V, and –2.5V rails are used in the audio and RF
sections.
D911 is a 4.096V (3%) reference diode. Its output is buffered by U906 which then
produces a reference voltage rail Vref, which is used by the CPU’s A/D
converter, and the
DACs, and also in the voltage to current converters of the
VCAs (see Sheet 4, and 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.
NB -2.5V is not used in the R50 receiver. In case, it is ever required in a future
release of the R50, it has been included in the schematic.
U915, though is not
fitted to the printed circuit board.
D911 is a 4.096V (3%) reference diode. Its output is buffered by
U906 which then
produces a reference voltage rail Vref, which is used by the CPU's A/D
converter, and the DACs.