Diodes are semiconductor devices with two terminals that allow current to flow in one direction. With a negligible resistance on one end and a high resistance on the other, diodes prevent current from flowing in both directions. As such, diodes work like a valve in an electrical circuit. Before outlining what diodes are and how they work, we must cover some basic terms to help you better understand the importance of diodes.
To begin, voltage is defined as the difference in electrical potential between two points. Resistors, on the other hand, are passive two-terminal electrical components that implement electrical resistance as a circuit element. Next, a capacitor is a passive component that stores electrical energy in an electrical field. Lastly, a transistor is a semiconductor device that contains three terminals for amplifying or switching electronic signals and other electrical power purposes.
While there are many different types of diodes, their basic construction remains the same. As diodes are semiconductors, they are either made of silicon or germanium. Their two terminals, an anode and cathode, are positioned on either side. The anode is the electrode where electricity flows in and the cathode is the electrode wherein electricity flows out. In the middle section, one can locate the P-N junction region that serves as the boundary between two types of semiconductor materials, P-type and N-type.
The basic working principle of diodes depends on the interaction between the P-N junction. In normal conditions, the P-type region has a high concentration of holes and a low concentration of free elections. Meanwhile, the N-type region contains a lower concentration of holes and a higher concentration of free electrons. These free electrons move towards the P-type region, allowing current to flow through the P-type region only. Now that we have defined how a diode operates under usual circumstances, the next section will provide a brief overview of two special scenarios.
A forward biased diode is produced when the positive terminal of a source is connected to the P junction while the negative terminal is connected to the N junction of the diode, and the voltage is slowly being increased from zero. As a result of the potential barrier, no current flows through at the beginning. In the case that the diode receives an external voltage that is larger than the forward potential barrier, the diode will act as a short-circuited path while the current will only be limited by external resistors.
Reverse biased diodes are generated when the voltage source is connected to the P junction’s negative terminal and the voltage source is connected to the N juntion’s positive terminal. This configuration produces the opposite effect of a forward biased diode. Due to electrostatic attraction, the holes in the P junction are shifted away from the depletion region, leaving uncovered negative ions in that area. As a result of this configuration, current flow is blocked in the circuit. Beyond such scenarios, diodes are also available in three common types: Zener, rectifier, and Schottky diodes.
Zener diodes are considered heavily-doped semiconductors as they allow current to flow in the opposite direction when exposed to ample voltage, unlike normal diodes. In particular, they are designed to break down voltage in a non-destructive way. Furthermore, due to their heavily-doped material, they enable the depletion region to be very thin in order to increase the intensity of the electric field.
Rectifier diodes are defined as two-lead semiconductors that allow current to flow in one direction. Usually made of silicon, they have the ability to convert alternating current (AC) into direct current (DC) via a process called rectification.
The last type of diode that will be covered is the Schottky diode. Considered metal semiconductor diodes, they have a similar appearance to rectifier diodes, but Schottky diodes are bigger and do not consist of a P-N junction.
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