Subaru XT 1988 Service Manual page 1183

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6-1 ENGINE ELECTRICAL SYSTEM
MECHANISM AND FUNCTION
Alternator (Ie Regulator)
The internal circuitry of the IC regulator is very complicated.
It consists of the following circuits.
(f(---
I
r---------
l
I
Y
I
I
coil
It(~-
31
, I
Field
III
coil
t1:
' (,-
I
: t
~ t
)
I
I
I
I
I
IC regulator
I
(f)
T
I
I BAT
I
-1-
e
'b
-~~
__
~ -~~
~---
- -
_ _ _ I
IC alternator
~
1)
- - - - - - - 2)
Fig. 1
1) Ignition switch ON (When engine is stopped)
When the ignition switch is turned "ON", the charge light
comes on and electric current (less than 0.5A) flows through
the field coil.
If the charge light does not come on when the switch is turned
"ON", it may be due to a burned-out charge I ight, a break in
the field coil, a defective Ie regulator, or improper contact
or wear of the brushes.
2) When the Ie alternator produces voltage (below regulation
voltage)
When the Ie alternator starts to generate, the charge light
goes out because the voltage at both ends of the light is equal.
On the other hand, field current is supplied from the diode.
When voltage at connection (a) of Rv·R t (the voltage-dividing
resistors which divide the voltage at the voltage detection
terminal
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is low, no current flows in Zener diode Dz and
2
- - . - - - 3)
L6-1650
transistor Trt is off. Therefore, the power transistor is on,
allowing field current to flow.
Even in this condition, if the voltage at terminal
@
exceeds
battery voltage, charging current flows to the battery.
3) When the IC alternator produces voltage (above regulation
voltage)
As the condition in 2) continues, voltage at terminal
©
builds up. Therefore, voltage at connection (a) increases. When
this voltage exceeds the voltage at which the Zener diode Dz
conducts, current flows through Dz and the transistor Trl'
The voltage at terminal
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at this time is called regulation
voltage (14.0 to 15.0V). In this condition, the power transistor
is off because Trt is on.
4) The alternator supplies electric current, repeating oper-
ations 2) and 3) to stabilize the voltage.