Axcera DT325B, Инструкция по эксплуатации

Страница: 43 / 65

350-Watt Digital VHF LB Transmitter Chapter 4, Circuit Descriptions
DT325B, Rev. 0 4-4
second serial potentiometer is
transferred through the first IC. The
wiper position of the digital
potentiometer circuit is used to set the
gain of the op-amp. Lower digital
values for the wiper settings increases
the gain of the op-amp. If N=0 then
Gain=6.0 and if N=255 then Gain=3.00.
If the Vin=1.0 at spare_Ain_1 and
N=128 then U21A out=4.0V with
gain=4. J62 and J63 are two 20
position connectors that provide the +12
VDC and –12 VDC power through the
Power Protection Board. The ±12 VDC
generated by the switching power
supply connects to J62 and J63 after
being fuse protected on the Power
Protection Board.
4.1.2.5 Schematic Sheet 5
There are three dual element,
red/green, common cathode LED
indicators mounted on the front panel of
the sled assembly that are used. The
fourth is a spare. The used LEDs are DC
OK, Operate and Fault.
There are four identical circuits, one of
which is a spare, that drive the front
panel mounted LED indicators. The
levels on the 1, 2, 3 and 4 LED Control
Lines, for both the red and green LEDs,
are generated by the IC U11, shown on
sheet 2, as controlled by the DATABUS
from the microprocessor U1, shown on
sheet 1.
Each LED controller circuit consists of an
N-Channel MOSFET w/internal diode that
controls the base of an N-P-N transistor
in an emitter follower configuration. The
emitter of the transistor connects the
LED.
With the LED control line LOW, the
MOSFET is Off, which causes the base of
the transistor to increase t12
VDC, forward biasing the transistor.
With the transistor forward biased,
current will flow from ground through
the LED, the transistor and the current
limiting resistors in the collector to the
+12 VDC source. The effected LED will
light.
With the LED control line HIGH, the
MOSFET is On, which causes the base of
the transistor go toward ground
potential, reverse biasing the transistor.
With the transistor reverse biased, no
current through the transistor and LED,
therefore the effected LED will not light.
A third color, amber, can also be
generated by having both transistors
conducting, both control lines LOW. The
amber color is produced because the
current applied to the green element is
slightly greater than the red element.
This occurs because the current limiting
resistors have a smaller ohm value in
the green circuit.
There are four voltage regulators, three
for +5 VDC, U26, U27 & U28, and one
for +7 VDC, U25, which are used to
power the Control Board. +12 VDC is
applied to U25 the +7 VDC regulator
that produces the (+7V), which is
applied to the LEDs mounted on the
board. The +7V is also connected to the
input of U26 a pre5.0 Volt
regulator. The +5.0Vdc regulator output
is used to power the analog circuits and
as the microcontroller analog reference
voltage (+5Vdc). Another two +5 Volt
regulator circuits U27, (+5V), and U8,
(+5Vserial), are used for most other
board circuits.
4.1.3 (A4) LCD w/Switches Board
(1307977; Appendix C)
The switch board provides five front-
panel momentary contact switches for
user control and interface with the front-
panel LCD menu selections. The
switches, SW1 to SW5, complete the
circuit through connector J3 to
connector J2 that connects to J1 on (A5)
the 20 Character by 4 line LCD Display.
J3 on the switch board is also cabled to
the (A3) System Controller Board.
When a switch is closed, it connects a
logic low to the system controller board