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The following summarizes the voltage and current relationships in this circuit:
12
=
0, therefore 1\
=
13
Vi -6V
6V - Vo
It
=""R88 =
13
=
R89
Since R88
=
R89, then V
0
=
12V - Vi
A similar analysis shows that the voltage at the other side of R91 is V
0
=
12V
+
Vi.
(12V- V i)-(l2V
+
Vi)
-2V·
1
Therefore, 10
=
= - - =
-2V i
1'--'
1----
In summary, for any voltage Vi' a current of -2V i runs through the actuator coils to generate a torque. For ex-
ample,
Vi
=
.5V
10
=
-1 amp (produces an outward torque)
10 flows from Ve ground end to V d then V c' Vb' and Va back to 24V.
When Vi
=
-1.5V, pin 4 of TDA2030 goes to 24V - Va (Vais a saturated transistor).
From Figure 1-16, Va
+
Vb
+
Vc
+
Vd
+
Ve
=
24V
When saturated Va :::: Ve :::: 1 _ - - (saturated output transistor of TDA2030)
~b
~
=
1'--' (R91)
10
10
24
10
10
13
= -
10
10::::
1.85A
@
25°C (produces an inward torque)
In summary, a positive Vi produces an outward motion (toward TKO) and a negative Vi produces an inward
motion (toward TKll71).
The transfer function of the actuator drive circuit is shown in Figure 1-17. In this circuit when V. is greater than
approximately .925V (at 25°C), 10 does not increase further because the voltage source is limited
10
24V.
REV A (01/84)
1-18
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