Power Supply; Front Panel And Display - Honeywell Bendix/King KX 165A Maintenance Manual

BENDIX/KING
4.2.6

POWER SUPPLY

Refer to figure 4-10 for the power supply block diagram. The unit uses a switching power supply
to generate voltages that supply the various electrical functions. The power supply converts 11-
33 VDC to 5 VDC, 9VDC, -12VDC, and -200 VDC. Refer to the power supply block diagram lo-
cated in figure 4-10. The 11-33 VDC aircraft bus is filtered via a hash filter. The output of the hash
filter goes to the transmitter and to the transformer. A switch connected to the transformer chops
the input voltage so the transformer can convert the input dc voltage to the several different volt-
ages. Each voltage output from the transformer requires a rectifier diode and filter capacitor to
complete the conversion to dc voltages. The -200 VDC line also has a post regulator in order to
accurately control the voltage that droves the display module. The output of the 9 VDC line is fed
back to the regulator IC which keeps the output voltages constant over varying loads. Before the
switching regulator stabilizes, a pre-regulator from the aircraft bus is used to supply power to the
regulator IC.
4.2.7

FRONT PANEL AND DISPLAY

The front panel display block diagram can be seen in
Module contain the display interface, knobs and buttons for pilot to enter data. The display inter-
face should receive signals from the main board and drive the gas discharge display. The knobs
and buttons' data will be sent to the microprocessor on the main board.
The front panel module has two dual concentric INC/DEC optical encoder switches with one pull
switch each, four push-button switches, two volume control pots with pull switches and one of the
volume controls has a rotary power on/off switch. The front panel buttons and switches are read
by periodically latching the state of the switches into the two parallel-to-serial converters/shift reg-
isters and shifting the data into the processor on the main board. The optointerrupter INC/DEC
switches consist of an IR LED and a phototransistor in a single package. In order for the IR light
to be detected by the phototransistor a metallic surface with alternating reflective and non-reflect-
ing surfaces is rotated in front of the photointerrupters.
The unit display is a segmented gas discharge display that is formatted as 24 cathode and 20 an-
ode buses. Each segment can be addressed by one combination of cathode and anode driver
line. The display is run by cycling through the cathode bus one at a time and turning on the ap-
propriate anodes. The display is updated by first sending the anode driver data and latching the
data into anode driver output latch. Then the cathode data stream is sent to the cathode driver
and then the DISPLAY ENABLE line is toggled. The cathode driver outputs are activated and the
display lights. This process is repeated for all 24 of the cathode buses on the display to complete
one full cycle of updating the display. The frame update rate of the display is approximately 70 Hz.
The front panel contains the potentiometers for the nav and com audio volume controls. The volt-
age on the wipers of the potentiometers are read by the A to D converters on the main board pro-
cessor which in turn control the volume by setting the digital pots on the main board.
The photocell is a variable resistor in which the resistance is dependent on the amount of light in-
cident to the photocell. When biased in a voltage divider configuration with another resistor the A
to D converter on the main board can read the changing voltage and change the intensity of the
display drive to track the existing light conditions.
Rev 0, Jun/2000
figure 4-9.
15610M00.RCD
The Front Panel and Display
Page 4-23
KX 165A