Forward & Reverse Bias Characteristics of PN Junction Diode

In an electrical device, the I-V Characteristic Curves are an established collection of graphical curves that are used to define its operation inside an electrical circuit. I-V characteristic curves, as the name implies, depict the relationship between the current flowing through an electrical device and the voltage applied across its terminals.

I-V characteristic curves are commonly used to determine and comprehend a component’s or device’s basic properties, as well as to mathematically model its behaviour inside an electronic circuit. We can exhibit a family or group of curves on the same graph to indicate the various values because there are curves representing the many inputs or parameters, as with most electronic devices.

The “current-voltage characteristics” of a bipolar transistor, for example, can be displayed with varying levels of base driving or the I-V characteristic curves of a diode working in both forward bias and reverse bias. 

However, a component’s or device’s static current-voltage characteristics do not have to be a straight line. As a linear or ohmic conductor device, we would anticipate the characteristics of a fixed value resistor to be generally straight and constant within specified ranges of current, voltage and power.

Ohmic & Non-Ohmic Conductors

Voltage and current have a linear relationship, according to Ohm’s Law. Ohmic conductors are conductors and electronic components that adhere to this law, whereas non-Ohmic conductors do not.

Ohmic conductors are also known as linear electronic components, whereas the others are non-linear since their voltage and current do not have a linear relationship.

It’s important to understand why some electronic components and conductors are Ohmic and obey Ohm’s law, while others are non-Ohmic and have a non-linear relationship between voltage and current while learning the fundamentals of electronics and many other aspects of electrical science.

Ohmic and non-Ohmic conductors are exemplified by the following instances.

Both Ohmic and non-Ohmic conductors can be found in abundance. Both are widely employed in electrical and electronic components and systems of all kinds.

I-V Characteristic Curves of an Ideal Resistor

At constant temperature, the affiliation between voltage and current in a pure resistance is linear and constant, such that the current I is proportional to the potential difference V times the proportionality constant 1/R, providing I = (1/R) x V. The current flowing through the resistor is then a function of the applied voltage, as shown by an I-V characteristics curve.

The resistor is a component that illustrates Ohm’s law’s linear relationship between voltage and current, i.e., V=I×R. Under some conditions, for example when exposed to high temperatures, practical resistors may display non-linear behaviour. Because the current flowing through a forward-biassed common silicon diode is restricted by the PN-ohmic junction’s resistance, semiconductor diodes have non-linear current–voltage characteristics.

I-V Characteristic Curves of Semiconductors

Semiconductor devices are all made up of semiconductor PN junctions that are coupled together and their I-V characteristics curves indicate how these PN junctions’ work. In contrast to resistors, which have a linear relationship between current and voltage, these devices will exhibit nonlinear I-V characteristics.

The basic function of a semiconductor diode, for example, is to convert AC to DC. A forward biassed diode will pass current if the greater potential is connected to the anode. The current is inhibited when the diode is conversely biassed (the greater potential is linked to the Cathode). This bias voltage also regulates the junction’s resistance and, as a result, the current flow across it.

I-V Characteristic Curve of a Diode

A forward or positive current travels through the diode when it is forward biassed, anode positive concerning the cathode and it operates in the top right quadrant of its I-V characteristics curves, as shown. The curve progressively climbs into the forward quadrant from the zero intersection, although the forward current and voltage are extremely modest.

When the forward voltage reaches the internal barrier voltage of the diode’s P-N junction, which is roughly 0.7 volts for silicon, an avalanche occurs and the forward current increases fast for a relatively tiny increase in voltage, resulting in a non-linear curve. The forward curve’s “knee” point.

When the cathode is positive about the anode and the diode is reverse biassed, it blocks current except for a small amount of leakage current and operates in the lower left quadrant of its I-V characteristic curves. The diode continues to block current flow until the reverse voltage across it exceeds its breakdown voltage point, resulting in a sharp spike in reverse current and a reasonably straight downward slope as the voltage losses control. Zener diodes make full use of this reverse breakdown voltage point.

Conclusion

The current-voltage characteristics of an electronic component reveal a lot about how it works. They can be a very useful tool in determining the operating characteristics of a device or component by displaying all of the possible current and voltage combinations and they can also be used as a graphical aid to better understand what’s going on in a circuit. For more information, you can even refer to the study material notes on forward bias and reverse bias.