: As
the aircraft
battery
e e
buss
voltage
will
rise,
when the voltage at the wiper
of
R11
(Regulator
Voltage Adjust) reaches
approximately
6.2
+
0.6
volts
=
6.8 volts, the input
transistor Q3
will
conduct.
Further
increases will
put
Q3 in
a
saturated
condition, with
its
collector
a
few
tenths
of
a
volt above the level set
by Zener
diode
CR4
(6.2 volts).
Rl4
and
RIS
are
both
2.AK
resistors.
With
the
collector of
Q3 at
about
+6.5
volts,
the junction of
R14-R15
will
try
to go
to about
-11
volts
below
the buss
voltage.
However,
the
base
of
Q4
will
catch this
at
-0.6
volts, effectively putting this transistor
into a saturated
condition.
The collector of
Q4,
and the base of
QB
will
now be about 0.3 volts below
the bums
voltage. This is sufficient
to
put
QS in
a
non-conducting
condition,
with
its
collector at
ground
potential. It
will
be
seen
that the
output
pair
Q6
and Q7
are
now
without forward
bias,
so
the
field
pin (B)
will
rest at
ground
potential.
Regulator
Repetition Rate
and
Rise
Times Under
average conditions,
the regulator
will
cycle
on and
off
at
about a 100
Hz
rate.
Also, the speed
at
which
the
unit switches is
carefully
controlled in order to reduce the
possibility of
high order
harmonics
causing
radio
frequency
interference
(RFI).
Capacitors
C-3,
C-4
and
C-5
reduce
the
overall
frequency
response
of
the unit,
which
limits the
switching
risetime
to around 200
microseconds.
C3 and
C4
function as an AC bypass to high frequency components
while
CS
adds
Miller
capacitance
between
the
collector
and base of
QS,
CRS is a
transient
protection
diode.
When the
current in
the inductive
field
circuit
is interrupted,
its
voltage
will
tend
to
collapse
to
zero
and
continue
in
the negative
direction.
The diode
CRS will
clamp this voltage
at
approxi-
mately
ground
potential.
3-10
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