Electronic Ignition Circuit Diagram

This electronic ignition circuit is intended to be inserted into a car's conventional ignition system. In
effect, it replaces tbe original I2-V switching circuit in tbe primary winding of tbe coil by one generating
more tban IOO V. It thereby converts a current circuit, which is upset by lead and stray resistance, into a
voltage circuit that is much more efficient.
The pulses emanating from the contact breaker, shown at tbe extreme lower left-hand side of the diagram,
are applied to transistor Tl and subsequently differentiated by R3/CI. This causes a negligible ignition
delay. The current through the contact-breaker points is determined by the value of Rl. This value has
been chosen to ensure tbat tbe points remain clean.
Transistor TI is followed by two monostables, !CIA and !CIB, which are both triggered by the output
pulses of Tl. However, whereas !CIA is triggered by tbe trailing edge, ICIB is triggered by the leading
edge.
Monostable !CIA passes a pulse of about 1.5 ms (determined by R4/C2) to NAND gate IC2A. This
gate switches off high-voltage Darlington T3 via gates IC2B, IC2C and IC2D, and driver T2, for the duration.
of tbe pulse. Gate IC2 ensures that T3 is switched on only when the engine is running, to prevent a
current of some amperes flowing through the ignition coil.
As long as pulses emanate from the contact breaker, I ClB is triggered and its Q output remains logic
high. The mono time of this stage is about I s and is determined by R5/C3.
Darlington T3 is switched on via T2 and IC2A through IC2D as long as !CIA does not pass an ignition
pulse. When the engine is not running, the Q output of IC2B goes low after I s and this causes T2 and T3
to be switched off. The two series-connected ISO-V zener diodes protect the collector of tbe BU932R
against too high of a voltage. The Darlington must be fitted on a suitable heatsink.
(Source: Encyclopedia of electronic circuits volume 4)