lgnition Operation Trigger Module (cont'd)
PRIMARY VOLTAGE WAVEFORM
Figure
53
As
the magnets rotate past the coil, voltage is produced.
This voltage, when uninterrupted, is first positive, then
negative as the magnet passes by the coil. This effect is
caused by the
two
opposing poles of the magnet.
Explanation of the trigger module also requires an
understanding of the
NPN
transistor. See Figure
54.
I
C
(Collector)
I
E
(Emitter)
NPN-type
Figure
54
A
transistor
has
a certain minimum voltage that
it
requires across the base and emitter (points
B
and E in
Figure
54
above) before
it
will "turn on". Once
it
has
turned on,
it
allows a small current,
l1,
to flow as shown
above. At
the
same time, the transistor allows a large
current,
12,
to
flow from point C to
E.
The magnitude of
current
l2
will vary in proportion to the smaller current,
l1.
Thus, the transistor functions
as
an amplifier in that
it
allows a small current to control a large one.
26
The following is the process the trigger module uses to
break the primary circuit to produce spark:
See
Figure
55
Figure
55
1.
The magnet passes by the coil and induces an
alternating voltage.
2.
As
the voltage begins to increase, (approximately
point "a"
in
Figure
53)
transistor
Tr2
is
turned on
and current flows from point
"C'
to
point
"D"
through
R3,
R4,
and Tr2. See Figure
56.
Figure
56
3.
Current
l1
flowing through Tr2 induces a larger
current
12.
Note that current
l1
is
very
small and
that
l2
is much larger. See Figure
57.
MTI
unit Ignition
coil
Ground
Spark
plug
4.
When the voltage
is
at the point
"a"
level as denoted
in "Figure
53,
Tr1 is still in the
off
mode
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