V-I Characteristics And SCR, MOSFET

V-I characteristics represent an electrical component’s voltage-ampere characteristics. It is described in the form of a graph. The V-I chart provides information about the Resistance and the functional area of an element. Thus, the graph breaks down an electronic component. The study of V-I characteristics of a component helps us determine where and how to use the component in an electric circuit.

An electronic component’s voltage-ampere characteristics represent the voltage and current behaviour for different values of applied voltage. In simple words, the V-I characteristics graph represents the measured current through an electronic component when a specific voltage is applied across it. 

Types of V-I Characteristics

In the V-I characteristics graph, the X-axis represents voltage V across the device and Y-axis represents the current I obtained for different values of applied voltage. Voltage is easier to control than current and becomes the independent variable. Thus, it is placed on the X-axis.

Based on the voltage-ampere graph, we can classify the V-I characteristics into two types.

Linear V-I Characteristics

The V-I characteristics graph with constant resistance and slope yields a linear V-I curve. The carbon resistors and metals apply Ohm’s law and thus, have constant resistance. Therefore, the V-I curve passes through the origin in a straight line. 

However, linear characteristics of an electronic component are found only in a particular region. For example, a diode’s operating region has a linear behaviour.

Non-Linear V-I Characteristics

A circuit component without constant Resistance possesses a non-linear V-I Characteristic. It is a function of current or voltage. 

For instance, the diode does not have constant Resistance for varied voltage values. However, for a small operating region, it shows linear characteristics.

V-I Characteristics of SCR

SCR or Silicon Controlled Rectifier’s voltage-ampere graph represents the current flowing through the SCR for the voltage applied across the anode to the cathode terminal.

SCRs are used to manage power flow rectification, inversion and regulation. It is a switching device containing a 3-terminal semiconductor.

The examination of V-I characteristics of SCR shows that it operates on three primary modes, they are:

• Forward Blocking mode

• Reverse blocking mode

• Forward conduction mode

Other aliases of SCR are thyroid transistors or thyristors.

V-I Characteristics of MOSFET

Metal Oxide Semiconductor Field Effect Transistor or MOSFET is a 3-terminal device where the voltage output controls the current flow between the source, drain and output terminals.

Thus, MOSFET has three terminals. They are

• Drain (D)

• Source (S)

• Gate (G)

The two types of power MOSFET Transistors are

• Enhancement Type 

• Depletion Type

V-I Characteristics of LED

“LED” or Light Emitting Diode is a forward-driven P-N junction diode developed strongly to convert electrical energy into optical energy. The LED comprises two leads. The shorter lead is for the n side and the longer lead is for the p side of the cathode. Gallium Arsenide connects the two junctions.

If the light is forward biassed, the non-metallised surface of the n region emits photons to the p regions. Thus, this increases the free carrier density at the junction. The excess free electrons join the free carriers on both sides. During recombination, the energy of emitted photons is equal to or slightly less than the bandgap.

The increasing current increases light intensity in forwarding Bias until it hits its threshold limit. Any further increase in current leads to a decrease in light intensity.

V-I Characteristics of P-N Junction Diode

The fusion of N-type material with the P-type material for creating a semiconductor diode is known as a P-N junction diode.

The graph of the P-N junction diode represents that the diode acts in 3 separate locations. They are:

• Zero Bias

• Forward Bias

• Reverse Bias

At Zero Bias, no external voltage is applied across the P-N junction diode. Thus, it suggests that the potential barrier stops the current passage.

At forwarding Bias, the p-type is connected to the positive terminal of external voltage and the n-type is connected to the negative terminal. This setup lowers the potential barrier. Thus, potential barriers fall and when the voltage is 0.7 V for silicon diodes and 0.3 V for Germanium diodes, the current flows.

When the P-N junction is in forwarding bias, the current intensity slowly develops and the curve is non-linear because the voltage applied has to overcome the potential barrier. 

After overcoming the potential barrier, the diode starts to act normal, and the curve ascends fast with an increasing external voltage. It thus creates a linear curve.

In reverse Bias, the P-type is connected to the negative terminal and the N-type to the positive terminal of the external voltage. As a result, there is an increase in the potential barrier. In addition, the presence of minority carriers at the junction leads to a reverse saturation current.

Conclusion

The V-I characteristics curve or voltage-ampere graph is a visual aid to knowing the device’s function and performance in the circuit. It helps to understand various electrical parameters of an electronic device. It also shows a device’s operating region for different values of voltage. Thus, the V-I characteristics graph helps determine the electronic component’s position and functioning in an electrical circuit.