Important Topic Of Physics: V-I Characteristics

V-I characteristics are the voltage-current characteristics of an electrical component or device. The V-I graph provides valuable information regarding resistance and deconstructs an electrical component. It also specifies a component’s operational area. We will learn where and how to employ a component in an electric circuit by examining its properties. An electrical component’s voltage-ampere characteristics describe its behaviour for various applied voltage levels. It is the graph generated when current is measured via an electrical component while a voltage is applied across it.

Types of V-I characteristics

Some of the different types are discussed below:

Linear V-I characteristics

A linear V-I curve has a constant slope and, as a result, a constant resistance. The V-I curve is a straight line that starts at the origin and ends at the destination. An electronic device exhibits linear character only in selective regions. For example, a diode shows linear V-I behaviour in its running region only.

Non-linear V-I characteristics

The resistance varies as a function of current or voltage. It shows linear characteristics only in a narrow portion of the graph; the major portion of the graph is non-linear. 

V-I characteristics of SCR

SCR is Silicon Controlled Rectifier. It is a three-terminal semiconductor switching device used as a control switch for rectification, regulation, and power flow inversion. At constant gate current, the V-I characteristic curve of an SCR is between the anode-cathode voltage, V, and the anode current, I. 

V-I characteristics of PN junction diode

A PN junction diode is obtained when an N-type material (excess free electrons) and a P-type material (extra holes) are fused. It is also called a semiconductor diode. There are three conditions for biassing based on the applied voltage.

Zero bias 

Zero bias is achieved when zero external voltage is applied to a PN junction diode. 

A Zero bias is otherwise known as an unbiased PN junction. Because no external voltage is given to the PN junction diode in this scenario, electrons diffuse to the P-side while holes diffuse to the N-side through the junction and mix. These charge carriers create an electric field as a result of this. The electric field prevents further charge carrier dispersion, resulting in no movement in the intermediate zone. This area is referred to as depletion width or space charge.

Forward Bias

Forward bias is achieved by connecting the positive terminal of the voltage potential to the P-type and the negative terminal to the N-type.

As the P and N-types are connected to the positive and negative terminals, forward bias will occur in the PN junction. In the event of being forward biassed, the electric field, both applied and built-in, will be in the opposite direction.

As the magnitudes of this built-in and generated electricity are combined, the electric field, which is generated, has less magnitude as compared to the built-in electric field. As a result, the depletion has low resistance, and the width narrows. The resistance of the depletion area becomes minimal when a large voltage is added. The silicon depletion zone’s resistance is negligible at 0.6 V, and current flows freely through it.

Reverse Bias

Reverse bias is achieved by connecting the negative terminal of the voltage potential to the P-type and the positive terminal to the N-type.

As the N and P-type are connected to the battery’s negative and positive terminal, the PN junction is reverse biassed. The applied and built-in electric field points in a similar direction in this scenario. 

When two of these fields are combined, the built-in and resultant electric fields have the same orientation; this results in a depletion region that is thicker and more resistive. When the applied voltage increases, it has a thicker and more resistive depletion region.

V-I characteristics of Zener diode

A Zener diode is an electronic device that operates in the Zener breakdown region. When these diodes are forward biassed, they behave similarly to PN junction diodes. Because they are extensively doped, these diodes have a minimal depletion area and can carry more electric current than normal PN junction diodes.

Zener diodes are categorised into two categories:

(i) Forward characteristics

(ii) Reverse characteristics

Importance of V-I characteristics 

It has a wide range of applications. Because it is light-sensitive, the PN junction diode may be used as a photodiode when reverse-biassed. It can be used for solar cells. PN junction diode has the potential to be used in LED lighting when it is forward-biased. It is used as a rectifier for electric circuits and a voltage-controlled oscillator in varactors. These are also helpful for the functioning of PN junction diodes.

Conclusion

V-I characteristics are known for the voltage-current features of an electrical component or device. V-I characteristics applications are helpful for the working of a PN junction diode. The PN junction diode, when reverse biassed, can be used as a photodiode because of its light sensitivity. This property makes them suitable for being used as solar cells. The diode shows LED lighting properties when forward-biassed.