Rectifier Diode Circuit Working And Its Applications

Diodes are widely used semiconductor device. A rectifier diode is a two-lead semiconductor that allows current to pass in only one direction. Generally, P-N junction Diode is formed by joining together n-type and p-type semiconductor materials. The P-type side is called the anode and the n-type side is called the cathode. Many types of diodes are used for a wide range of applications. Rectifier diodes are a vital component in power supplies where they are used to convert AC voltage to DC voltage. The Zener diodes are used for voltage regulation, preventing unwanted variations in DC supplies within a circuit.

Symbol of a Diode

The symbol of a rectifier diode symbol is shown below, the arrowhead points in the direction of conventional current flow.

Rectifier Diode Symbol
Rectifier Diode Symbol

Rectifier Diode Circuit Working

Both the n-type & p-type materials are chemically combined with a special fabrication technique which results in the formation of a p-n junction. This P-N junction has two terminals which can be called as electrodes and due to this reason, it is called to be a “DIODE “(Di-ode).

If an external DC supply voltage is applied to any electronic device through its terminals, it is called as Biasing.

Unbiased Rectifier Diode

  • When no voltage supplied to a rectifier diode then it is called as an Unbiased Diode, N-side will have a majority number of electrons, and very few numbers of holes (due to thermal excitation) whereas the P- side will have a majority charge carriers holes and very few numbers of electrons.
  • In this process, free electrons from N-side will diffuse (spread) into the P side and recombine takes place in holes present there, leaving +ve immobile (not moveable) ions in N- side and creating -ve immobile ions in the P side of the diode.
  • The immobile in the n-type side near the junction edge. Similarly, the immobile ions in the p-type side near the junction edge. Due to this, numbers of positive ions and negative ions will accumulate at the junction. This region so formed is called as depletion region.
  • At this region, a static electric field called as Barrier Potential is created across the PN junction of the diode.
  • It opposes the further migration of holes and electrons across the junction.
Unbiased Diode (No Voltage Applied)
Unbiased Diode (No Voltage Applied)

Forward Biased Diode

  • Forward Biasing: In a PN junction diode, the positive terminal of a voltage source is connected to the p-type side, and the negative terminal is connected to the n-type side, the diode is said to be in forwarding bias condition.
  • The electrons get repelled by the negative terminal of DC voltage supply and drift towards the positive terminal.
  • So, under the influence of applied voltage, this electron drift causes current to flow in a semiconductor. This current is termed as “Drift current”. As majority carriers are electrons, current in n-type is the electron current.
  • As holes are majority carriers in p-type, these get repelled by positive terminal of DC supply and move across the junction towards the negative terminal. So, the current in p-type is the hole current.
  • So, the overall current due to majority carriers creates a Forward current.
  • The direction of conventional current flows from positive to negative of battery in the direction of conventional current is opposite to the electrons flow.
Forward Biased Rectifier Diode
Forward Biased Rectifier Diode

Reverse Biased Diode

  • Reverse Biased condition: if the diode is the positive terminal of the source voltage is connected to the n-type end, and the negative terminal of the source is connected to the p-type end of the diode, there will be no current through the diode except reverse saturation current.
  • This is because at the reverse biased condition the depletion layer of the junction becomes broader with increasing reverse biased voltage.
  • Although there is a small current flowing from the n-type to p-type end in the diode due to minority carriers. This current is called Reverse Saturation Current.
  • Minority carriers are mainly thermally generated electrons/ holes in p-type semiconductor and n-type semiconductor respectively.
  • Now if reverse applied voltage across the diode is continually increased, then after certain voltage the depletion layer will destroy which will cause a huge reverse current to flow through the diode.
  • If this current is not externally limited and it reaches beyond the safe value, the diode may be permanently destroyed.
  • These fast moving electrons collide with the other atoms in the device to knock off some more electrons from them. The electrons, so released further release much more electrons from the atoms by breaking the covalent bonds.
  • This process is called as carrier multiplication and leads to a considerable increase in the flow of current through the p-n junction. The associated phenomenon is called Avalanche Breakdown.
Reverse Biased Diode
Reverse Biased Diode

Some Applications of Rectifier Diode

Diodes have many applications. Here are a few of the typical applications of diodes include:

  • Rectifying a voltage, such as turning the AC into DC voltages
  • Isolating signals from a supply
  • Voltage Reference
  • Controlling the size of a signal
  • Mixing signals
  • Detection signals
  • Lighting systems
  • LASER diodes

Half-Wave Rectifier

One of the most common uses for the diode is to rectify the AC voltage into a DC power supply. Since, a diode can only conduct current one way, when the input signal goes negative, there will be no current. This is called a half-wave rectifier. The below figure shows the half wave rectifier diode circuit.

Half-Wave Rectifier
Half-Wave Rectifier

Full-Wave Rectifier

  • A full wave rectifier diode circuit builds with four diodes, by this structure we can make both halves of the waves positive. For both positive and negative cycles of the input, there is a forward path through the diode bridge.
  • While two of the diodes are forward biased, the other two are reverse biased and effectively eliminated from the circuit. Both conduction paths cause current to flow in the same direction through the load resistor, accomplishing full-wave rectification.
  • The Full-wave rectifiers are used in power supplies to convert AC voltages to DC voltages. A large capacitor in parallel with the output load resistor reduces the ripple from the rectification process. The below figure shows the full wave rectifier diode circuit.
Full-Wave Rectifier
Full-Wave Rectifier

Thus, this is all about Rectifier Diode and its uses. Do you know any other diodes that are regularly used in real-time electrical and electronics projects?  Then, please give your feedback by commenting in the comments section below. Here is a question for you, How the depletion region is formed in a Diode?

 

2 Comments

  1. Sandesh Pradhan says:

    Dear Sir

    On Diode, the article written & narrated is too good.
    If you need an article on Uninterrupted Power Supply (UPS), I can provide.
    What will be the remuneration you provide to a writer?
    I am an Electronics M Tech from IIT-MUMBAI, with 36 yrs of Industrial experience.

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