What are diodes and how diodes are used in alternators and automotive applications

What are Diodes

Diodes are devices which will allow the flow of electricity in one direction, it is simply a one-way valve and if the current tries to reverse the flow of direction the diode won’t allow it. The current flow will be blocked

Most modern diodes are semiconductor diodes which have p-n junction the p-type side is the anode and the n-type side is the cathode. The diode is the most used semiconductor material in an electronic circuit. An intrinsic semiconductor is in between the two terminal of the diode and is doped by impurities

P-N junction diode

A p-n junction diode is used for the operation in forwarding direction which will allow the current flow in one direction and blocks the flow in opposite direction the n-type material will receive electrons and the p-type material will lose the electron and there will be holes a semiconductor diode can be constructed by simply joining the n and p-type material


P-N junction operation in forward and reverse bias

The electrons in n-type material will attract to the positive terminal of the source and the holes to the negative terminal. Thus the depletion region becomes bigger and the electrons cannot pass so any current flow.

Electrons in n-type material will attract to the positive terminal of the source and jumps to p-type material, while the holes in p-type material are attracted towards the negative terminal of the source and jump to n-type material thus the depletion layer becomes lesser or it may be gone and electrons can pass hence current flow

Diodes in alternators

Alternators use nine diodes six diodes are in the rectifier bridge and three in the diode trio, these diodes turn the spinning action of the alternator and its alternating current into direct current, if one of the diodes fails then it will affect the performance of the charging system

Diodes in automotive applications

Light-emitting diodes are designed to produce light, LED’s are just like normal diodes because they won’t pass current that won’t go against it. in much automotive application LED’s are used for example in many vehicles it is used as day time running lights


Diodes are used to bridge solenoids which are used in vehicles. Diodes are placed across many coils they are installed in reverse bias position to block B+ and therefore the current passes through the coil when the B+ is turned off the magnetic field of the coil collapses including the current flow in the coil and this current passes through the diode since the current is in the same direction as the diode arrow, which was previously blocking the B+ and this current flow induced in the electric field of the coil allows to collapse itself. A spark is not produced and the ECM is protected against damage