Electronics is playing an important role in many fields of electrical engineering. With its evolution, electronics are being involved in almost all electrical equipment. The rectifier is such branch of electronics in which alternating current is converted into direct current. There are many applications of rectifiers, for example, computers, laptops, mobile chargers, etc.

What will You Learn in this Article?

  • What is PN Junction?
  • Biasing of PN Junction:
  • What is Diode?
  • Diode as a Rectifier
  • Full Wave Rectifier using center-tapped Transformer
  • Full wave Bridge Rectifier Circuit

What is PN Junction?

Junction means a point where two or more two circuit elements are combined. So, A PN junction is such an area where P-type and N-type semiconductors are combined to form the junction as shown in figure 1.1.

As in P-type semiconductors holes are majority charge carriers and in N-type semiconductors electrons are in majority, so when both types of semiconductors are combined, the process of filling the gaps (holes) started until a layer known as the “depletion layer” is formed as shown in figure 1.2. As the name, depletion; suggest that charge in that area is depleted, therefore no charge exists on the depletion layer. When the formation of the depletion layer comes into existence, a difference of potential is created across the depletion layer which is known as the “potential barrier”.  The value for the potential barrier changes with the semiconductor materials used. For example, the value for the potential barrier for Ge is 0.3V and for Si is 0.7V. Potential barrier means that value of potential is at least required across the PN junction for the flow of electric current through it.

PN Junction

Fig 1.1: PN Junction

PN Junction with deletion layer

Fig 1.2: PN Junction with deletion layer

Biasing of PN Junction:

The process of connecting a PN Junction with the supply is called biasing. There are two types of biasing:

  1. Forward Biasing
  2. Reverse Biasing

Forward Biasing

When the P side of a PN junction is at higher potential with respect to its N side, PN Junction is called forward biased. In simple words, when the positive terminal of supply is connected with the P side of PN Junction and the negative terminal of supply is connected with the N side of PN Junction; a PN Junction is called forward biased.  A simple circuit showing the forward biasing of a PN Junction is shown in figure 1.3. During forward biasing of a PN junction, the depletion layer is reduced and current flows from P  to N side in circuit.

Forward Biasing of PN Junction

Fig 1.3: Forward Biasing of PN Junction

Reverse Biasing

When P side of a PN junction is at lower potential with respect to its N side, PN Junction is called reverse biased. In simple word, when positive terminal of supply is connected with N side of PN Junction and negative terminal of supply is connected with P side of PN Junction; a PN Junction is called reverse biased.  A simple circuit showing reverse biasing of a PN Junction is shown in figure 1.4. During reverse biasing of a PN Junction, depletion layer is widened and no current flow in circuit.

Reverse Biasing of PN Junction

Fig 1.4: Reverse Biasing of PN Junction

What is Diode?

A diode is a bi-terminal component that allows the current to pass through it only in one direction. A simple diode is a PN junction with two terminals named: anode and cathode. The symbol for a diode is shown in figure 1.5

Diode Symbol

Fig 1.5: Diode Symbol

Biasing of a Diode

The process of connecting a diode with the supply is called biasing. There are two types of biasing:

  1. Forward Biasing
  2. Reverse Biasing

1. Forward Biasing:

When the anode is at higher potential with respect to the cathode, the diode is called forward biased. In simple words, when the positive terminal of supply is connected with anode and the negative terminal of supply is connected with cathode; a diode is called forward biased.  A simple circuit showing the forward biasing of a diode is shown in figure 1.6. During forward biasing of a diode, the depletion layer is reduced and current flows from anode to cathode in the circuit as explained in the first quadrant of the V-I graph shown in figure 1.8.

Forward Biasing of a diode

Fig 1.6: Forward Biasing of a diode

1. Reverse Biasing:

When anode is at lower potential with respect to the cathode, the diode is called reversed biased. In simple words, when the negative terminal of supply is connected with anode and the positive terminal of supply is connected with a cathode; a diode is called reverse biased.   A simple circuit showing the forward biasing of a diode is shown in figure 1.7. During reverse biasing of a diode, the depletion layer is widened, and the current does not flow from anode to cathode in the circuit as explained in the third quadrant of the V-I graph shown in figure 1.8.

Reverse Biasing of a diode

Fig. 17: Reverse Biasing of a diode

V-I characteristic curve of a diode

Fig. 1.8: V-I characteristic curve of a diode

Diode as a Rectifier

The process of converting alternating current into the pulsating direct current is called “rectification”. Such a circuit that converts alternating current into the pulsating direct current is called a “rectifier”. A diode is used as a rectifier in two configurations which are:

  1. Half wave Rectifier
  2. Full wave Rectifier

Half wave Rectifier

Such a circuit that converts only half cycle of alternating current into pulsating dc voltage is called a halfwave rectifier.

Working of Half wave Rectifier

Biasing diagram of a half-wave rectifier and its input AC waveform are shown in figures 1.9 and 1.10, respectively. When a positive half cycle is reached at the anode, the diode is forward biased and with the reduction of the depletion layer, the current is allowed to pass through diode. The positive half cycle is received at the load as shown by the oscilloscope in figure 1.11. When a negative half cycle is reached at the anode, the diode is reversed biased and with the expansion of the depletion layer, the current is not allowed to pass through the diode. The zero voltage is received at the load as shown by the oscilloscope in figure 1.11.

Half wave rectifier circuit

Fig 1.9: Half wave rectifier circuit

Input AC waveform

Fig 1.10: Input AC waveform

Output waveform of Halfwave rectifier

Fig 1.11: Output Waveform of Halfwave Rectifier

Full wave Rectifier

Such circuit which converts the complete cycle of alternating current into pulsating direct current is called a halfwave rectifier. A full wave rectifier is further classified into two types:

  1. Full wave rectifier using center-tapped transformer.
  2. Full wave Bridge Rectifier Circuit

1. Full Wave Rectifier using center-tapped Transformer:

Biasing diagram of a full wave rectifier circuit is shown in figure 1.12. When positive half cycle is reached at anode of diode-1 (D1), the D1 is forward biased and D2 is reverse biased; with the reduction of depletion layer, current is allowed to pass through diode D1. The positive half cycle is received at the load as shown by oscilloscope in figure 1.13. When positive half cycle is reached at anode of diode-2 (D2), the D2 is forward biased and D1 is reverse biased; with the reduction of depletion layer, current is allowed to pass through diode D2. The positive half cycle is received at the load as shown by oscilloscope in figure 1.13.

Full wave rectifier circuit using center-tapped transformer.

Fig 1.12: Full wave rectifier circuit using center-tapped Transformer

Output waveform of full wave center-tapped rectifier

Fig 1.13: Output waveform of full wave center-tapped Rectifier

2. Full wave Bridge Rectifier Circuit

Biasing diagram of a full wave bridge rectifier circuit and its input waveform are shown in figures 1.14 and 1.15, respectively. When positive half cycle is reached at anode of diode-1 (D1) and negative half cycle is reached at anode of diode-3 (D3), the D1 & D3 are forward biased and D2 & D4 are reverse biased; with the reduction of depletion layer, current is allowed to pass through diodes D1 and D3. The positive half cycle double in magnitude is received at the load as shown by oscilloscope in figure 1.16. When positive half cycle is reached at anode of diode-2 (D2) and negative half cycle is reached at anode of diode-4 (D4), the D2 & D4 are forward biased and D1 & D3 are reverse biased; with the reduction of depletion layer, current is allowed to pass through diodes D2 and D4. The positive half cycle double in magnitude is received at the load as shown by oscilloscope in figure 1.16.

Full wave bridge rectifier circuit

Fig 1.14: Full Wave Bridge Rectifier circuit

Input AC waveform

Fig 1.15: Input AC waveform

Output waveform of bridge rectifier circuit

Fig 1.16: Input AC waveform