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8.1
.
3
Regulator
Board A ( RGA )
Regulator
Board A is the
+
5 V
regulator
for all functions
requiring logic
level
supplies
within the APR
-
5000
transport
.
The
input to
the RGA Board is
+
14 V unregulated no load
.
This
is
received via connection CNJ 960
on pin 3
.
The
+
14 VDC is
fed into the
input of
the LM 309 K
or
LM 2940
through resistor
R
2 and
D 3
.
Capacitors C
2 and C 3
perform decoupling
for both
high
and low
frequencies
.
Transistor Q 2 is used
as a
pass
element to increase the current capabilities of the LM 309 K
or
LM 2940
.
Bias
voltage
is set from the combination of R 3 and
the network of R 2 and D 3
.
The
input
of the
LM 309 K
or
LM 2940
acts as a
base reference for transistor
Q 2
.
o
Capacitor
C 4 is used
as a
filter and to allow slow
ramp
on of
the circuit
.
Q 1 is
part
of
an
indicator circuit
showing a
short circuit
condition of the RGA Board
power output
(
either internal
or
external to the RGA )
.
Under normal
operating
conditions the
bias of D 2 emitter of Q 1
to
the base of Q 1 (
R
2 and
D 3 )
is
such that Q 1 is turned off
,
thus no current flow
through
diode
D
1
.
If
an over
-
voltage
condition would exist
,
the bias of Q 1
would
change
,
thus increasing
the VBE
on
Q 1
causing
LED D
1 to
1
ight
.
change
in bias
on
the
gate
and its network
of
D 7
, R
5 and R
6
.
In addition
,
the triac Q
4
would conduct due to the
o
If
an
external
short to ground
would
exist
,
the
LM 309 K
or
LM 2940 would exhibit its own
internal thermal
limiting and
diode D
would
light through
the conduction of
Q 1 being
turned
If
a
short
was present on the output
less the
ground
on
•
(
negative voltage
)
,
D 6 would conduct and
the
crowbar circuit
of Q 4 would activate
.
respective
devices create
a reverse voltage protection
.
Diodes D 4 and D 5 around their
In addition
,
the RGA
board feeds
+
14 V to the Power
Distribution Board ( PDB ) which is used
by
the
power
down
imminent circuit
( PDI
signal
)
.
The fuse for the
+
5 V
power
supply
is also mounted
on this PC
board
.
n
N
_
_
8
-
2
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