Diodes are two-terminal semiconductor electronic components that allow current to flow in one direction while blocking it in the opposite direction. They play a vital role in various electronic applications, from rectifying alternating current (AC) to direct current (DC) to protecting electronic circuits from damage.
A diode is made of two semiconductor layers joined together to form a p-n junction. These two semiconductor layers are created by doping pure silicon with different elements.
When two P-type and N-type semiconductor layers come into contact with each other, a p-n junction is created. At the p-n junction, electrons from the N layer diffuse into the P layer, combining with the holes there. This process creates a depleted region where there are neither free electrons nor holes. Due to the diffusion of electrons from the N layer to the P layer, the N layer will be positively charged and the P layer will be negatively charged. The potential difference between the two semiconductor layers is called the diffusion potential. This diffusion potential creates an electrical barrier, preventing the current from moving in the opposite direction.
The terminals of the diode are known as the anode (A) which corresponds to the P region and the cathode (K) corresponds to the N region.
Diode approximation is a mathematical method used to approximate the nonlinear behavior of real diodes to enable calculations and circuit analysis. There are three different approximations used to analyze the diode circuits [1].
First Diode Approximation
In the first approximation method, the diode is considered as a forward-biased diode and as a closed switch with zero voltage drop. It is not apt to use in real-life circumstances but used only for general approximations where preciseness is not required.
Second Diode Approximation
In the second approximation, the diode is considered as a forward-biased diode in series with a battery to turn on the device. For a silicon diode to turn on, it needs 0.7V. A voltage of 0.7V or greater is fed to turn on the forward-biased diode. The diode turns off if the voltage is less than 0.7V.
Third Diode Approximation
The third approximation of a diode includes voltage across the diode and voltage across bulk resistance, RB. The bulk resistance is low, such as less than 1 ohm and always less than 10 ohms. The bulk resistance, RB corresponds to the resistance of p and n materials. This resistance changes based on the amount of forwarding voltage and the current flowing through the diode at any given time.
The voltage drop across the diode is calculated using the formula
Vd = 0.7V + Id *RB
And if RB < 1/100 RTh or RB < 0.001 RTh, we neglect that
Diodes are classified into different types based on their structure, function, and applications. Some common diode types include:
Silicon Diode (Si Diode): The most common diode type, used in various electronic applications.
Schottky Diode: A type of diode with fast switching speeds, often used in high-frequency electronic circuits.
Zener Diode: A type of diode with voltage stabilization capabilities, commonly used in power supply circuits.
LED (Light Emitting Diode): A type of diode that emits light when current passes through it, used in LEDs and displays.
Laser Diode: A type of diode that emits laser light, used in applications like optical disc readers and laser cutters.
Diodes are widely used in various fields, including:
Rectification: Diodes are used to convert AC to DC, providing power for electronic devices.
Circuit Protection: Diodes are used to protect electronic circuits from damage caused by reverse voltage or overcurrent.
Signal Control: Diodes are used to control electronic signals in circuits.
Indication: LEDs are used as indicator lights to show the operating status of electronic devices.
Optical Sensors: Diodes are used in optical sensors to detect light or infrared radiation.
When selecting a diode, consider the following factors:
Diode Type: Choose the diode type suitable for the specific application.
Maximum Voltage: Select a diode with a maximum voltage higher than the voltage used in the circuit.
Maximum Current: Choose a diode with a maximum current greater than the current that needs to pass through the diode.
Switching Speed: Select a diode with a switching speed that matches the operating frequency of the circuit.
Size and Shape: Choose a diode with a size and shape that fits the installation space.
Reference:
[1] El-Pro-Cus, What is Diode Approximation: Types and Diode Models, https://www.elprocus.com/diode-approximation-types-and-diode-models/
