Transistorised Ignition System | Construction , Diagram , Working

Transistorised Ignition System | Construction , Diagram , Working

Transistorised Ignition System

A transistor interrupts a relatively high current carrying circuit, i.e, it controls high current in the collector circuit with less current in the base circuit. Therefore, a transistor is used to assist the work of a contact breaker. Hence, this system is known as Transistorassisted ignition system or transistorized ignition system.


It consists of battery, ignition switch, transistor, collector, emitter, ballast resistor, contact breaker, ignition coil. distributor and spark plugs. The emitter of the transistor is connected to the ignition coil through a ballast resistor. A collector is connected to the battery.


The cam in the distributor is rotated by the engine. It opens and closes the contact breaker points.

Transistorised Ignition System
Transistorised Ignition System

When the contact breaker points are closed:

1. A small current flows in the base circuit of the transistor.
2, A large current flows in the emitter or collector circuit of the transistor and the primary winding of the Ignition coil due to the normal transistor action.
3. A magnetic field is set up in the primary winding of the coil.

When the contact breaker points are Open :

1. The current flow in the base circuit is stopped.
2. The primary current and the magnetic field in the coil collapse suddenly due to immediate reverting of the transistor to the non-conductive state.
3. It produces a high voltage in the secondary circuit.
4. This high voltage is directed to the respective spark plugs through tho rotor of the distributor.
5. This high voltage produces a spark when it is tried to jump the spark plug gap. It ignites air-fuel mixture in the cylinder.

Advantages :

  1. It increases the life of contact  breaker points.
  2. It gives high ignition voltages . 
  3. It gives longer duration of sparks .
  4. It has very accurate control of timing.
  5. It needs less maintenance.

Disadvantages :

  1. More mechanical points are needed similar to a conventional system.
  2. It has a tendency to side tracking .

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Sachin Thorat

Sachin is a B-TECH graduate in Mechanical Engineering from a reputed Engineering college. Currently, he is working in the sheet metal industry as a designer. Additionally, he has interested in Product Design, Animation, and Project design. He also likes to write articles related to the mechanical engineering field and tries to motivate other mechanical engineering students by his innovative project ideas, design, models and videos.

3 thoughts on “Transistorised Ignition System | Construction , Diagram , Working

  1. Does anyone make a transistorized point assist ignition module anymore?
    I need one for a 12 volt negative ground. Just want the points to last longer.

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