Rectification


Alternating current is suitable for both heating and lighting because the heating effect of a current is independent of its direction.

However, in many practical systems, the use of alternating current will not be possible. For example, in large motors and electric railway systems, we will need the operating current to flow in one direction consistently and alternating current is not able to fulfil that criterion.

But direct currents are harder to generate than alternating currents and alternaing voltages are more convenient to step up and to step down, the process of converting a.c. to d.c. by a rectifier is important.


Rectification is the process in which an alternating current is forced to only flow in one direction.

  • Done using diodes since diodes could only allow current to flow in one direction only.

 

A diode is an electrical device that permits current to flow in one direction only. It is forward biased if connected the other way round and little or no current flows.

Half-wave Rectification:

Halfwave.rectifier

 

From the circuit shown in the image, a diode is connected to the circuit. Since the diode only allows current to flow in ONE direction, the current in the other direction will be zero (recall that the direction of current flow in A.C. reverses periodically). This means that half of the power is lost in half-wave rectification.

 

Full-wave Rectification:

Full wave rectification

From the circuit shown in the image, 4 diodes are connected to the circuit. It might seem confusing at first but it is incredibly simple. Walkthrough of the current flow in full-wave rectification circuit:

  • Since the diodes are arranged in a vertical straight line, we shall label them as 1, 2, 3, 4 with 1 being the top diode and 4 being the bottom diode. Let’s start with the top part of the circuit where the current path immediately branches out to two diodes with opposite direction (diode 1 and 3)
  • We’ll start with the current flowing towards the right. Diode 1 will allow the current to flow while diode 3 will not.
  • After passing through diode 1, the current will encounter diode 2 and the resistor (load). Since diode 2 will block the current from flowing through, the current will then pass through the resistor.
  • After passing through the resistor, the current reaches another crossroad (diode 3 and diode 4). The current will not flow through diode 3 even though the direction is correct. This is because current does not flow from low potential to high potential. (After passing through the resistor, the current will have a potential loss).
  • Hence, the current will flow through diode 4 and complete the circuit.
  • You can repeat this for the other direction of A.C. flow.

 


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