Resistance of a Diode

Encyclopedia
08/28/2024

Diode Resistance


Resistance opposes the flow of current through a device. Diode resistance is the effective opposition a diode offers to current flow. Ideally, a diode offers zero resistance when forward biased and infinite resistance when reverse biased. However, no device is perfect. Practically, every diode has small resistance when forward biased and significant resistance when reverse biased. We can characterize a diode by its forward and reverse resistances.

 


Forward Resistance


Even with forward biasing, a diode won’t conduct until it reaches a minimum threshold voltage. Once the applied voltage exceeds this threshold, the diode starts to conduct. The resistance offered by the diode in this condition is called forward resistance. In other words, forward resistance is the resistance a diode shows when it is forward biased.

 


Forward resistance is classified into two types viz., static or dynamic depending on whether the current flowing through the device is DC (Direct Current) or AC (Alternating Current), respectively.

 


6af85f113d185002324c8a1c177cbc01.jpeg

 


Static or DC Resistance


It is the resistance offered by the diode to the flow of DC through it when we apply a DC voltage to it. Mathematically the static resistance is expressed as the ratio of DC voltage applied across the diode terminals to the DC flowing through it (shown by the black dotted line in Figure 1) i.e.

 


ae175f38cd947358d23b4c415e319d81.jpeg

 


Dynamic or AC Resistance


Dynamic resistance is the resistance a diode offers to AC current when connected to a circuit with an AC voltage source. It is calculated as the ratio of the change in voltage across the diode to the change in current through it.

 


683a0b8d97ca6403a917969603e6e967.jpeg

 


Reverse Resistance


When we connect the diode in reverse biased condition, there will be a small current flowing through it which is called the reverse leakage current. We can attribute the cause behind this to the fact that when the diode functions in its reverse mode, it will not be completely free of charge carriers. That is, even in this state, one can experience the flow of minority carriers through the device.


Due to this current flow, the diode exhibits reverse resistance characteristic which is shown by the purple dotted line in Figure 1. The mathematical expression for the same is similar to that for the forward resistance and is given by

 


Where, Vr and Ir are the reverse voltage and the reverse current respectively.

 


263e2c3476fbfa616370da3d04bb7a64.jpeg

 


After knowing the basic facts about the diode resistance, it is important to note the fact that“Generally the diodes have a high ratio of reverse to forward resistance, which makes them essentially unidirectional in function”.


Encyclopedia

The Electricity Encyclopedia is dedicated to accelerating the dissemination and application of electricity knowledge and adding impetus to the development and innovation of the electricity industry.

Does a grid-connected inverter need a grid to operate?
Does a grid-connected inverter need a grid to operate?
Grid-connected inverters do need to be connected to the grid to function properly. These inverters are designed to convert direct current (DC) from renewable energy sources, such as solar photovoltaic panels or wind turbines, into alternating current (AC) that synchronizes with the grid in order to feed power into the public grid. Here are some of the key features and operating conditions of grid-connected inverters:The basic working principle of grid-connected inverterThe basic working principl
Encyclopedia
09/24/2024
Advantages of infrared generator
Advantages of infrared generator
Infrared generator is a kind of equipment that can produce infrared radiation, which is widely used in industry, scientific research, medical treatment, security and other fields. Infrared radiation is an invisible electromagnetic wave with a wavelength between visible light and microwave, which is usually divided into three bands: near infrared, middle infrared and far infrared. Here are some of the main advantages of infrared generators:Non-contact measurement No contact: The infrared generato
Encyclopedia
09/23/2024
What is a Thermocouple?
What is a Thermocouple?
What is a Thermocouple?Thermocouple DefinitionA thermocouple is a device that converts temperature differences into an electric voltage, based on the principle of the thermoelectric effect. It is a type of sensor that can measure temperature at a specific point or location. Thermocouples are widely used in industrial, domestic, commercial, and scientific applications due to their simplicity, durability, low cost, and wide temperature range.Thermoelectric EffectThe thermoelectric effect is the ph
Encyclopedia
09/03/2024
What is a Resistance Temperature Detector?
What is a Resistance Temperature Detector?
What is a Resistance Temperature Detector?Resistance Temperature Detector DefinitionA Resistance Temperature Detector (also known as a Resistance Thermometer or RTD) is an electronic device used to determine the temperature by measuring the resistance of an electrical wire. This wire is referred to as a temperature sensor. If we want to measure temperature with high accuracy, an RTD is the ideal solution, as it has good linear characteristics over a wide range of temperatures. Other common elect
Encyclopedia
09/03/2024
Inquiry
Download
Experts Electrical is dedicated to serving the personnel in the global power industry.
Join Experts Electrical, not only can you discover power equipment and power knowledge, but also canhnd like - minded friends!