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b.
c.
The
emitter
of
the pass
transistor
supplies the load through
Rl2.
If
the
current
drawn
through
Rl2
is
excessive,
the
volt-
age drop across
Rl2
will
exceed the forward voltage necessary
to
cause
Q4
to
conduct.
When
Q4
conducts,
it
fires
SCR
CR3
which
shorts
out the reference thereby causing the supply
to
shut
down.
When
this
occurs,
Cl
starts
to
charge through
Rll.
When
the voltage
at
the junction
of
Rll
and
Cl
becomes
more
negative than the gate voltage
of
SCR
CRl,
CRl
fires
discharg-
ing Cl.
The
resulting
pulse causes
Ql
to
momentarily
interrupt
the holding
current
through
CR3
thereby
cutting
off
CR3.
This
action
resets
the supply automatically.
15
Volt Regulator
Zener diode
CR6
is
the reference for
this
regulator.
Q5
and
Q7
amplify the voltage across
this
diode
to
approximately
15
volts.
Q6
acts
similar
to
Q4
if
the current
drawn
from
the supply ex-
ceeds approximately
100
ma.
5 Volt Regulator
A 6.3
volt
zener diode
CR5
is
the reference for
this
regulator.
QB
buffers the voltage a~ross
this
diode
and
drives the chassis
mounted
pass
transistor
AlQ2.
Q9
and
R25
provide the
current
limit
function for
this
supply.
The
limit
point
is
approximate-
ly
500
ma.
-14-
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