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Honeywell King Bendix FULL MAINTENANCE MANUAL KC 140
FLIGHT CONTROL SYSTEM. 341 bookmarked indexed searchable pages.
MANUAL NUMBER 006-15573-0000
This section contains the block diagram and detailed theory for the KC 140 flight computer.
There are four boards in the flight computer -- Power Supply Board, Main Board, Accelerometer Board, and the Display Board. The Main Board contains the bulk of the circuitry of the flight computer.
The Power Supply board, as the name indicates, has the power supply circuitry. The Accelerometer
Board (Only in two-axis flight computers) contains the accelerometer and associated circuitry for the desired output gain. The Display Board contains the display and mode switches.
This section gives a high-level description of the circuit theory of operation for the KC 140.
The Power Supply Board contains five power supplies: 5V logic, 5V audio, 15 V analog, 15 V DG power, and -185 V display power. It also provides a filtered aircraft voltage, 5V analog (VDDA),
4 V baro reference supply (VDDS), and -75V and -175 V display driver bias voltages. Refer to
figure 4-1. Input Surge Protection
Aircraft power and Audio power are filtered and surge-protected in separate circuits. Each circuit limits the maximum voltage to about 34 volts. The filtered, protected aircraft voltage output is provided to the 5V logic supply and to the rest of the unit. The filtered, protected audio voltage is provided
to the 5V audio power regulator. 5V Logic Power Supply
The filtered aircraft power (11-34 VDC) is stepped down to 5 VDC by a switching regulator. This voltage is supplied to the logic circuitry on the other boards. An additional pi filter is used to provide an analog 5V (VDDA) with reduced ripple. This voltage is further filtered by a low-dropout regulator
to provide a low-noise 4V reference voltage (VDDS) for the remote baro set potentiometer and the internal pressure sensor. 5V Audio Power Supply
The filtered audio power is regulated and filtered to provide a 5V power for audio alerting circuitry. 15 V Power Supplies
The 5V logic power is supplied to dual identical 15 VDC power supply modules, one provides
power for internal analog circuitry and the other external DG power. Separate supplies are used to provide independence due to the restricted current capabilities (30 mA) of each module. -185 V Display Power Supply
A flyback regulator is used to provide -185 VDC display power. Low-voltage shutdown and overcurrent limiting is provided. A buffered resistive divider and zener diode provide -75 VDC and -175 VDC for use in the display driver circuitry.
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