Notes

The objective of this article exercise is to demonstrate how to model a physical system using Simscape blocks.

A circuit will be created to study the VI characteristics of a diode and to plot the results using the Scope Block. We will also learn how to connect electrical blocks in a circuit and how to connect voltage and current sensors.



Theory

A forward-biased diode conducts current (IF) in the forward direction. The relationship between forward voltage and forward current is the ampere-volt, or IV characteristic, of a diode. In the following figure, you can see an example of a typical forward IV characteristic for a diode.

Forward Characteristics

The observations are as follows −

Voltage is measured across a diode, while current is measured through it.

A forward voltage of 0V across the diode results in 0 mA of forward current (IF).

As VF is increased progressively from the beginning point (0) of the graph IF begins to increase.

When VF exceeds the barrier potential of the P-N junction, IF increases considerably. This is known as the knee voltage VK. Diodes made of germanium have VK of approximately 0.3 V; silicon diodes have VK of approximately 0.7 V.

Increasing voltage above the value of VK tends to make the forward current quite large.

This operation causes excessive heat to build up across the junction, which can destroy the diode. To avoid this situation, a protective resistor is connected in series with the diode. This resistor limits the forward current to its maximum rated value. Normally, a current-limiting resistor is used when diodes are operated in the forward direction.







By performing DC sweep analysis, VI characteristics can be determined. The applied voltage is vary from an initial value of 0 to a stop value of 1 V.






The positive supply is connected to the anode and a negative supply to the cathode of the PN Semiconductor diode is called Forward Bias. Increase the +ve supply to anode, the depletion region width decrease and conduction of electron increase.