Tandy 1000 SL Technical Reference Manual page 319

F i n a l i n t e r n a l s t e p
p u l s e i n U1
n
SOD o u t p u t
I
I
A p p l i e d v o l t a g e t o
motor c o i l s
4V,approx.
ov
*-------
I - ----
( F i g . 2 1 2 ) S t e p p i n g motor o v e r d r i v e t i m i n g
O v e r d r i v e c i r c u i t 2
The SOD s i g n a l
i s
s u p p l i e d t o t h e o v e r d r i v e c i r c u i t 2 c o n s t r u c t e d by
U3 ( p i n s 2-15) a n d PNP t r a n s i s t o r
43
a n d i t makes Q3 t u r n on w h i l e t h e
SOD s i g n a l
is
H I G H l e v e l . +12V power
i s
a p p l i e d t o t h e s t e p p i n g motor
c o i l s a t t h a t t i m e t o e x e c u t e t h e s e e k a n d s e t t l i n g o p e r a t i o n s s e c u r e l y
w i t h h i g h t o r q u e .
A f t e r t h e c o m p l e t i o n of t h e s e t t l i n g , o n l y +5V power i s s u p p l i e d t o t h e
c o i l s t h r o u g h t h e d i o d e CR2 which minimize t h e power
loss
by s u p p l y i n g
o n l y t h e r e q u i r e d t o r q u e
f o r
h o l d i n g t h e s t o p p o s i t i o n . By t h e above
d e s i g n , h e a t r a d i a t i o n
is
d e c r e a s e d t o t h e minimum l e v e l a n d t h e power
consumption
of
t h e s t e p p i n g motor i n s e e k s t o p i s o n l y 0.25W, a p p r o x .
-
240
-