Suzuki DF 25, Service Manual, Page: 40 / 148

IGNITION AND ELECTRICAL 3-3
OPERATION
The transistorized ignition circuit will be discussed by referring to the diagram below:
When the recoil starter is pulled, the flywheel is turned. An electromotive force generated in the primary
winding (n
1
) of the ignition coil makes the transistor (TR
1
) conduct through the resistor (R
1
) and forms the pri-
mary circuit (indicated by dashed lines).
As the flywheel turns further, the primary current increases, and the terminal voltage of the circuit consisting
of the resistor (R
1
) and transistor (TR
1
) increases. This increases the working voltage at the connection of
the series circuit (R
2
and R
3
) connected in parallel to the primary circuit. As the flywheel turns further, the ter-
minal voltage of the resistor (R
3
) in the resistor circuit (R
2
and R
3
) rises to the level of working voltage of the
transistor (TR
2
) when the ignition timing approaches, and thus the transistor (TR
2
) is turned on. As a result,
the base current of (TR
1
) flowing through the resistor (R
1
) is by-passed, and the transistor (TR
1
) is turned off
from the conductive state.
The current flowing through the primary winding (n
1
) is thus interrupted, and a rapid change occurs in the
magnetic flux across the ignition coil. The result is a high surge voltage in the secondary winding (n
2
).
TRANSISTOR
R
2
R
3
TR
2
TR
1
R
1
FLYWHEEL
MAGNETO
IGNITION
COIL
SPARK
PLUG
EMERGENCY/
ENGINE STOP
SWITCH
S
N
n
1
n
2