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4-28
PROTECTION CIRCUIT
4-29 This c i r c u i t prevents the high voltage doubler
from e x c e e d i n g approximately 4kV which might oc-
cur if the f e e d b a c k loop were t o malfunction.
Diodes CR37 and CR38 a r e connected d i r e c t l y
a c r o s s t h e control winding and rectify (monitor)
the voltage aGross t h i s winding.
The rectified
voltage c h a r g e s c a p a c i t o r C24, and when i t ex-
c e e d s a predetermined l e v e l , neon tube VR3 fires.
The resulting positive going voltage turns on Q17
which in turn s h o r t s t h e control winding of trans-
former T1, t h u s , reducing the output of t h e high
voltage doubler.
Overvoltage control R71 deter-
mines the l e v e l a t w h i c h VR3 w i l l fire and, there-
fore, controls the maximum output voltage of the
high voltage doubler.
4-30 REFERENCE REGULATOR
4-31 This circuit supplies regulated d c b i a s volt-
a g e s t o the voltage input c i r c u i t and t15V program-
ming voltage t o the voltage control circuit. Diodes
CR22 through CR25 and c a p a c i t o r C16 rectify and
filter t h e 43 Vac developed a c r o s s the secondary
of T2.
The 56 Vdc is regulated b y transistor Q12
which is controlled by Q13 a n d VR1.
The t15V
programming voltage is developed b y c o n s t a n t cur-
rent amplifier Q14-Q15 which
is
connected t o the
-40V reference voltage.
Resistors R51 and R52 a r e
s e l e c t e d t o provide p r e c i s e l y t h e correct program-
ming current.
Procedures for s e l e c t i n g t h e s e re-
s i s t o r s are included in the adjustment and calibra-
tion paragraphs in Section V, Maintenance.
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