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

BENDIX/KING
The unit also makes available the aircraft power bus as an output that is controlled by the on/off
switch. Q1044 is turned on when the Power ON* line goes low.
LOC ENERGIZE* goes low when Q1017-A is turned on; this is used to signal external equipment.
Q1019 goes low in order to turn on the internal glideslope receiver.
Audio Alert* goes low in order to activate a sound device such as a sonalert or other audio annun-
ciator.
4.3.6

POWER SUPPLY

A flyback power supply is used to supply all of the low level power requirements. It consists of a
hash filter, flyback transformer, rectifier/filters, current mode controller and power switch, a post
regulator for the display voltage and on-off switch circuitry.
Aircraft power is applied to the hash filter, C1208, C1209, C2140, C1266, C1282, C1288,
CR1042, L1020 and L1021. These components attenuate noise coming in on the 11-
33_VDC_POWER line and switching noise from the flyback regulator. CR1042 suppresses tran-
sients on the 11-33_VDC_POWER line.
The Flyback transformer consists of T1003. When Q1045 is turned on, energy is stored in the
primary of T1003. This energy is dumped into the rectifier capacitors when Q1045 is turned off.
The Rectifiers/Filters consist of CR1048, C1210, C1311 and C1312 (-200V), CR1051 and C1226
(-12V), CR1059 and C1269 (+9V), and CR1058 and C1252 (+5V).
The Current Mode Controller and switch consists of U1036, Q1045 and associated components.
The switching frequency of the supply is 125.0 kHz. The power supply reference frequency is 125
kHz. This 125 kHz signal is derived from a 500 kHz ceramic oscillator, Y1002, and inverter U1024.
U1026 divides the 500 kHz signal down by 4 before it is fed to inverter U1007-F and then to U1036
pin 4.
R1341 and C1280 are parts external to U1036 that set the frequency of oscillation until the supply
has reached proper output voltage and synchronization is provided from the digital circuitry on the
Main Board. The output of the +9V rectifier is feed back to U1036 via R1295, R311 and R1312. If
this voltage is higher than the reference voltage (pin 8 of U1036) the peak current of the switch
(Q1045) is reduced by reducing pulse width of the drive (U1036 pin 1) to the switch thereby low-
ering the output voltage of the +9V rectifier. U1036 senses the peak current through the switch
by monitoring the voltage across R1319 and R1320. R1345 and C1290 attenuate high frequency
noise that comes from the switch and CR1067 reduces the voltage needed across R1319 and
R1320 in order to reach the level required by U1036. R1314, R1316 and CR1064 limits the max-
imum pulse width. A soft start feature is provided by C1264. R1312, R1313 and C1278 provide
compensation for the power supply feedback loop.
The on-off switch circuitry consists of two current sources and a switch, all of which are turned on
by the front panel on-off switch providing a short to ground. The current sources (Q1040 and
Q1041 and associated components supply current to U36 until the soft start capacitor (C264) has
charged to 1.95 volts. Above this voltage U1036 pin 13 sinks current to ground turning off Q1041.
Q1040 supplies enough current to drive the Q1041 current source but not so much that U1036 pin
13 cannot turn off Q1041. If all is working normally, the voltage to U1036 pin 14 will be supplied
by the +9V power supply output when the soft start is complete and U1036 pin 13 turns off Q1041.
If the +9V output has not reached the required regulated voltage, the soft start will begin again.
This cycle will be repeated until the +9V voltage reaches the required value. If the power supply
is overloaded for any reason (any of the outputs drawing too much current) the supply will contin-
ually go through the soft start cycle until the overload is removed.
4.3.7

FRONT PANEL AND DISPLAY MODULE

The front panel board has two connectors. P2011 comes from the main board and J2012 goes to
the display module. The display signals that control the anode driver are DOTCLOCK (P2011-
Rev 0, Jun/2000 15610M00.RCD
KX 165A
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