Circuit
Operation:
Relay Kl is normally
de-energized
and the
contacts
F
and
G
are
closed.
These contacts connect the aircraft buss
to the regulator
section when the typical external connections
are
made
as
shown.
Zener diode CR2, and
its biasing resistor,
R7,
sets
the emitter
of
Ql
at
5.1 volts below
the
buss
level.
Under
normal operating conditions
the
voltage divider Rl,
R2,
R3
will
set
the
base of Q1
slightly
more positive
than
its emitter,
therefore,
Ql
will
be
non-conducting
and its collector
will
be at ground potential.
If
the
collector of Ql is at zero, the
base
of
Q2 must also be
at zero, therefore,
Q2
is
non-conducting with
its
collector at the
buss voltage
and
relay
Kl
is de-energized.
Diode CR1 will
be
reverse-biased
by
about 4
volts.
Circuit
Operation
During Overvoltage
Condition: When the voltage
at pin
A
approaches
the
tripout level,two
actions
take place. (1) The
voltage at the base
of
Ql
will rise in
the
ratio determined by
Rl,
R2,
R3.
Typical
settings
will
present about
80%
of the
voltage
change
to the
base
of
Ql,
(2) 100% of the voltage change at pin
A
will be
coupled through
Zener
diode
CR2
to
the
emitter
of
Ql,
therefore,
the oyerall voltage
change
between
Ql base and emitter
will
be
in the direction of
turn-on.
When
Ql turns
on, its
collector
will
rise and bring
Q2
into
conduction by supplying a
current
path
through divider RS, and
R6.
With
Q2
conducting,
its collector
will
be near ground,
effectively
completing
the
relay
circuit (Kl).
Relay
Hold-In:
Once the
relay
is
energized,
it
will
be held
in by
the
following
actions.
(1)
When
the collector
of Q2
goes
to within a
few
tenths of a volt
of
ground,it will place the
previously
reverse-biased
diode
CR1
in a conducting
condition.
Current through R9 and
CRl
will now
add
to
3-13
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