BFGoodrich Avionics Systems,
Inc.
Component Maintenance Manual
P/N
501-1075-()
D. Power
Regulation
And Output
The
28Vdc
applied
to
connector pin
13 is divided
by
the network
consisting of
resistors AlR12
and
AlR13,
and
zener
diode
AlCR8.
Transistor AlQ6
will
conduct as
longas
the
iriput
voltage to
pin
13
exceeds
20Vdc. Transistor
AlQ6
completes the path for current
flow
through
zener
diode
AlCR10,
diode AlCR11
and
resistor
AlR15.
This
biases transistor A1Q7to an
ON
condition
that,
in
turn, completes
current
paths
for transistor A1Q8.
The DC
voltage at
transistor
A1Q9
collector must reach 16 VDC before regulation begins. No
voltage
appears on transistor AlQ11
and
AlQl3
collectors until transistor AlQ9
is
turnedON.
When
input voltage exceeds 16Vde,
zener
diode CR9 passes
current to transistor
A1Q9.The
voltage appears on transistor AlQ9emitter
and
divides across resistors AlR16, AlR17 and
AlRl8.
The arm
of
resistor A1R17 connects
transistor A1Q7base to
the voltage
divider and
AlQ7
conducts.
Transistor
A1Q7turns transistor AlQ8ON.
Transistor
AlQ9
now
conducts
and
the DC line
voltage
is applied to the output transistors AlQll
and
AlQ13. The voltage on
transistor AlQ9emitter is adjusted by resistor AlR17 to remain
at
23.5Vdc. Changes in load
or aircraft
bus voltage change the
conduction of
transistor
A1Q9to compensate.
The
square
wave
developed across
transformer T1
(described in
paragraph 2)
is
applied
to the
bases
of transistors A1Ql0,A1Q11,
A1Ql2
and
AlQl3.
The
polarity is such
that
transistors
Q10and
Ql3conduct
simultaneously
on one half-cycle and
transistors AlQll
and AlQl2 on
the other
half-cycle. Current flow on each half-cycle
will
cause
a
voltage drop
across
transformer
T2. Terminal
T2-1
is positive when transistors AlQ11
and
AlQ12conduct, and
terminal
T2-2
is positive
when
transistors A1Ql0and A1Q13
conduct.
The secondary of
transformer
T2 provides
the l
l5Vac,
26Vac
and
4.5Vac
outputs to the
connector.
E.
Start/Run Power
Added shifted
phase
voltage is
provided
by
a time
delay
circuit
consisting
of
transistors
AlQ14,
AlQl5,AlQl6
and
AlQl7.
When DC
voltage
is applied,
current flow
begins
through
capacitor
A1C8 and
resistors AlR23,
A1R24 and AlR38.
As
capacitor AlC8 charges,
current
flow
decreases and transistor Q14
base
becomes
more negative.
As
transistor
AlQ14base
becomes negative
it
will
conduct
and connect transistor
AlQ15base
to a more
negative
voltage. Transistor
AlQl5 begins to
divert
the current through
transistor AlQ16.
Transistor
AlQl6
collector becomes
more
negative until transistor AlQl7
gate
is no
longer
positive
enough to conduct.
This removes
capacitor A1C9
from the
circuit and the
shifted-phase
voltage is
reduced.
F.
Battery Isolation And
Charging
The
voltage
divider
described in
paragraph
3
biases transistor
AlQ6to
an ONcondition. The
battery charging potential
through
A2CRl 6 and
A2CR17 applied
by A2R33 and A2R34 to
bias
A2Ql9
and A2Q20OFF. As
long
as
aircraft 28.0Vdc
is
applied
to
connector pin 10,
transistors A2Q18
and A2Q20
are OFF
and the batteries
are
isolated from the
emergency
bus,
pin
11. If aircraft 28Vdc
is
interrupted,
transistors
A2Ql8and A2Q20
will connect
the
internal
batteries to the
emergency
bus. A2CR24 and
A2CR25 provide
battery
isolation.
Battery
charging results
from
tapping and
rectifying part of
the
output
voltage. Transformer
T2, terminals 8 and
10, and diodes
A2CR16
and A2CRl7
provide approximately 40Vdc
while
the
inverter
is operating.
The
charging
current
is
approximately 145mA fromthe inverter
charger and
45 mA from the external
28Vdc.
The
external
path
through
A2CR22
allows
a
trickle
charge although
the inverter
may be OFF, as
is often
the case
during
periodic inspection.
msmijtp202DescriptOpsdiskl59
24-20-03
Page 6
Revision
A
June 30, 1999
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