Characteristics of PN Junction Diode

Characteristics of PN junction diode is a graph between the voltage applied across its terminals and the current that flows through it. It is drawn to know the behavior of diode in the electrical circuit.

For a typical junction diode, characteristics are shown in Figure. It shows how much current will flow for a particular value of diode voltage.

characteristics of pn junction, characteristic of pn junction diode

Forward Characteristics of PN Junction Diode

To obtain the forward bias characteristics of PN junction diode, set up the circuit shown in Figure.

In the circuit, a DC battery is connected to the diode through a potentiometer.
The potentiometer helps in varying the voltage applied to the diode. The milli-ammeter measures the current in the circuit. The voltmeter measures the voltage across the diode.

forward characteristics of pn junction diode, characteristics of p-n junction

Here, the voltage is plotted along the x-axis, as the voltage is the independent variable. Each value of diode voltage produces a particular current. The current, being the dependent variable, is plotted along the y-axis.
From the curve, we know that the diode current is very small for the first few tenths of a volt. The diode does not conduct well until the external voltage overcomes the barrier potential.
As we approach 0.3 V, a larger number of free electrons and holes start crossing the junction. Above 0.3 V even a small increase in the voltage produces a sharp increase in the current.
A forward voltage, at which the current through the junction starts to increase rapidly, is known as knee voltage (Vo) of the diode.
For a germanium diode, it is approximately 0.3 V, whereas for a silicon diode it is about 0.7 V.
If too large current flows through the diode, excessive heat will destroy it. The maximum current that a diode can handle safely is specified by the manufacturer.

Reverse-Bias Characteristics of PN Junction Diode

To obtain the reverse-bias characteristics of PN junction diode make the following changes:

  • reverse the terminals of battery and note that high voltage battery is used here ,
  • replace the milli-ammeter with a micro-ammeter.
characteristics of junction diode

In the reverse bias, the diode current is very small. It is only a few µA for germanium diodes and a few nA for silicon diodes.
It remains small and almost constant for all voltages less than the breakdown voltage (Vz).  At breakdown voltage, current increases rapidly for a small increase in voltage.

A reverse voltage, at which PN junction breaks down with a sudden rise in reverse current is known as the breakdown voltage of the diode.
The high reverse current may damage the junction. Therefore, for proper operation of a junction diode, reverse voltage across a PN junction should always be less than the breakdown voltage.

Limiting Values of Junction Diode

Every PN junction diode has three limiting values;

  • Maximum Forward Current: It is the highest instantaneous forward current that a junction diode can conduct safely.
  • Peak Inverse Voltage (PIV): It is the maximum reverse voltage that can be applied to a junction diode without damage to the junction. If the reverse voltage across the diode exceeds its PIV, the diode may be destroyed due to excessive heat.
    The peak inverse voltage is very significant when we are using diodes in rectifier circuit. In such applications, reverse voltage across diode during negative half-cycle of AC should not exceed the PIV of a diode.
  • Maximum Power Rating: It is the maximum power that can be handled by a diode safely. It is equal to the product of junction current and voltage across the junction.

For safe operation of a diode, these values should not be exceeded. If these are exceeded, a diode may be destroyed due to excessive heat. These are specified by the manufacturer in the data sheets.

Related Posts

  1. P N Junction Diode Theory | Working
  2. Characteristics of PN Junction Diode
  3. Working Principle of Rectifier
  4. Zener Diode Characteristics
  5. Zener Diode as Voltage Regulator
  6. JFET | Junction Field Effect Transistor Basics
  7. JFET Construction and Working
  8. Op Amp | Operational Amplifier Basics
  9. Transistor as a Switch
  10. Buck Converter Working
  11. Buck Boost Converter Working
  12. Astable & Monostable Operation of 555 Timer Chip
  13. Light Sensitive Devices
  14. Industrial Applications of Ultrasonic Waves
  15. Radar Working Principle
  16. Electrical Timer & Timer Charts
  17. RLC Parallel & RLC Series Circuit Resonance
  18. Types of Capacitors

© forward and reverse bias characteristics of pn junction diode.

1 thought on “Characteristics of PN Junction Diode”

  1. Arc flash study is very crucial in power systems. An arc flash is a phenomenon where a flash-over of electric current leaves its intended path and travels through the air from one conductor to another, or to ground. The results are often violent and when a human is in close proximity to the arc flash, serious injury and even death can occur. Arc flash can be caused by many things including: Dust, Dropping tools, Accidental touching, Condensation, Material failure, Corrosion, Faulty Installation.

    The factors to determine the severity of an arc flash injury are Proximity of the worker to the hazard, Temperature, fault current and Time for circuit to break. The main objective of an arc flash study is to identify and analyze high risk arc flash areas in your electrical power system with greater flexibility by simulating and evaluating various mitigation methods in arc flash study.

    Know More

Leave a Comment

Your email address will not be published. Required fields are marked *