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o F a i l - S a f e C i r c u i t
When low source voltage or some other problem with
the deck mechanism prevents the solenoids from operating,
or if the mode switching detector switch fails to operate,
the system shuts down to prevent current flow from
c o n t i n u i n g t o t h e s o l e n o i d . l f a p p r o x i m a t e l y 3 s e c o n d s
a f t e r t h e s o l e n o i d h a s c o m e o n , a n d s w i t c h T 1 - T 3 h a v e n o t
c o m e O N , P D 1 0 0 4 g o e s i n o p e r a b l e a n d a l l o u t p u t s a r e d i s -
abled. Also, no inputs except RST will be accepted.
The amount of time prior to activation of the fail-safe
c i r c u i t i s d e t e r m i n e d b y t h e t a n k c i r c u i t ( C 5 , R 2 7 1 c o n n e c t -
e d t o t h e T C p i n ( p i n 2 1 ) . T h e T C p i n i s t h e o u t p u t f r o m
an n-channel open-drain transistor with a hysteresis gate
i n p u t w i t h o u t p u t n o r m a l l y p u l l e d l o w w h e n O N . W h e n a
key entry produces solenoid output, the TR goes OFF and
the open TC pin allows C5 to start charging through R27.
S O L E N O I D
n - 1 3
T C
( P D r O 0 4 P r N 2 r )
o lnitial Reset
Initial reset is connected to the power switch through
b o t h R 3 8 , C 7 a n d R 3 7 , D l 1 . W h e n t h e p o w e r i s t u r n e d
O N , t h e l e v e l w i l l b e h e l d l o w f o r t h e c h a r g i n g t i m e o f R 3 8 ,
C 7 a n d a l l c o n t e n t s o f l C P D 1 0 0 4 a r e c l e a r e d . W h e n t h e
Consequently, TC pin voltage rises with the time constant
ot R27, C5, but if one of the mode switching detector
switches fi-T3l
comes ON prior to reaching the high
level threshold of the hysteresis gate (within the lC), the
n - c h a n n e l T R i s t u r n e d b a c k O N , a n d t h e c h a r g e o f C 5
quickly passes back through R31 dropping the voltage level
a t t h e T C p i n a n d d i s a b l i n g t h e f a i l - s a f e c i r c u i t .
lf a malfunction prevents switches Ti-T3
from coming
ON after solenoid operation, TC pin voltage will exceed the
h i g h t h r e s h o l d o f t h e h y s t e r e s i s g a t e w i t h i n t h e l C , c a u s i n g
t h e f a i l - s a f e c i r c u i t t o o p e r a t e a n d c u t a l l o u t p u t s O F F .
F o r t h e l C t o s t a r t o p e r a t i n g a g a i n , t h e R S T p i n w i l l
h a v e t o r e c e i v e a l o w i n p u t , f o l l o w e d b y a h i g h . I n o t h e r
words, power will have to be turned OFF, then back ON.
F i g . 2 1
P O W E R
O N
P O W E R
O F F
o
O N
O F F
@
O F F
O N
P O W E R
S W I T C H
0 n O i
* O l
o ' r
I
o *
|
I
v ,
v t
I
I
I
t
- G r . R
s w r r c H
v - - - - -
I S q ; P O W E R
I
s w r r c x
n
F i g . 2 2
p o w e r i s t u r n e d O F F , t h e p o w e r s w i t c h a l l o w s t h e c h a r g e o f
C 7 t o q u i c k l y p a s s t o g r o u n d t h r o u g h R 3 7 a n d D 1 1 , m a k -
i n g r e s e t a n e x t r e m e l y q u i c k a n d e r r o r f r e e o p e r a t i o n .
A C T I V E
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