electronic car ignition circuit

Electronic car ignition circuit


This scheme is for 4 cylinder motor. This will make your car
spent less fuel, be a little bit faster and you wont have to
frequently open your distributor cap to change the contact
buttons thus wasting less money.

T1/T2 create one monostable multivibrator in which C2 and R5
determine the length of impulse which is 1,5 msec. Next in line
are T3 and then T4 which is Darlington transistor specially
developed for electronic ignition which is used as a switch to
turn on/off primary coil. Impulses from switch P turn on
monostable multivibrator T1/T2. You need to un-connect capacitor
that is in distributor cap because it is not needed anymore.
While switch P is closed T1 is in off state but T2 is in on
state, also T3 and T4 which enables current to flow trough
primary coil. When switch P is opened, T1 gets in on state for a
moment causing C2 to charge over R6 which makes T2 go to off
state because of voltage drop on R6. When T2 is off also T3 and
T4 are off and current that was flowing trough primary coil is
stopped. Because T2 is in off state, voltage on R8 is
increased which is passed trough R5 on T1 base which is still in
on state and C2 is still charging. After 1,5 msec. C2 value
reaches the level where T2 goes to on state again and T1 goes to
off state. Now T2, T3 and T4 are in on state, again, and current
flows trough primary coil again. R2 and D1 are used to neutralize
the effect of impulses caused from «jumping» of switch P which
could turn on monostable multivibrator when it shouldn`t.

Zener diodes Z5 and Z6 are together with R10 limit overcharged
voltage impulses that are caused by self induction of primary
coil which could damage T4. They should be connected as close as
possible to T4.

D7 protects device from wrong polarity.

Coil should have ratio of 1:80 or 1:100 with external resistor
Rv which is used for better cooling. Total resisting value (Rp)
of primary coil and Rv resistor shouldn`t be under 1,6 ohm`s so
current trough T4 wouldnt be bigger than 10A.

Depending on Rp, R9 have different values:

120Ω/2W for Rp tot > 2,2Ω

100Ω/2W for 1,8Ω < Rp tot < 2,2Ω

82Ω/3W for 1,5Ω < Rp tot <1,8Ω

T4 has to be heatsinked!!!

All resistors are 1/2W +/-5%


D1-D4 = 1N4148

D5-D6 = BZX85C 180 (replicable with all equivalent types with power of 1,3W)

D7 = 1N4001

R1 = 470 – 1W

R2 = 22k

R3 = 2,2k

R4 = 1k

R5 = 4,7k

R6 = 39k

R7 R10 = 100

R8 = 680

C1 C2 = 47nF (ceramic)

C3 = 0,22uF 400V (ceramic)

C4 = 100uF (electrolytic)

T1 T2 = BC327 (BC327-25, BC327-40)
T3 = BC237B (BC547B, BC547C)

T4 = BUX37 (BU323, BU920, BU921, BU922, BUV37B (u TOP3),
BUW29, BUW81, MJ10012, MJ10013, MJ10014, TIP662, TIP665, 2SD683)

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