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A diode is a two-terminal device that permits just one direction of electric current to pass. As a result, it functions similarly to a check valve or a one-way street in the electronic world. It’s a device that converts an Alternating Current (AC) to a Direct Current (DC) (DC). A semiconductor material (semiconductor diode) or a vacuum tube are used to make it (vacuum tube diode). The majority of diodes nowadays, however, are constructed of semiconductor materials, mainly silicon.

A. Structure

There are two types of diodes: vacuum diodes and semiconductor diodes, as previously stated. Two electrodes (cathode and anode) are put inside a vacuum glass tube to form a vacuum diode. P-type and n-type semiconductors are used in semiconductor diodes. As a result, it’s called a p-n junction diode. Silicon is the most common material, however germanium or selenium can also be used.

B. What Is It and How Does It Work?

When a filament heats the cathode, an unseen cloud of electrons known as space charge accumulates in the vacuum. Although electrons are emitted from the cathode, they are repelled by the negative space charge. No current passes via the circuit because electrons cannot reach the anode. The space charge dissipates when the anode is made positive. Current begins to flow from the cathode to the anode as a result. As a result, electric current travels only from the cathode to the anode and never from the anode to the cathode within the diode.

Diode with a P-N Junction

A p-n junction diode is made up of p-type and n-type silicon semiconductors. Boron is commonly doped into p-type semiconductors, resulting in holes (positive charge). On the other hand, an n-type semiconductor is doped with antimony, which adds a few additional electrons (negative charge) to it. As a result, electric current can pass between the two semiconductors.

When you combine p-type and n-type blocks, the n-additional type’s electrons join with the p-holes type’s to form a depletion zone with no free electrons or holes. In other words, current cannot flow via the diode.

When the negative terminal of the battery is connected to n-type silicon and the positive terminal is connected to p-type silicon (forward-bias), current begins to flow because electrons and holes can now pass across the junction. No current flows through the diode if the terminals are reversed (reverse-bias), since holes and electrons are pushed apart from each other, enlarging the depletion zone. A junction diode, like a vacuum diode, can only allow current to flow in one direction.

C. Purpose and Importance

Though diodes are one of the most basic components in an electronic circuit, they have a wide range of applications.

The rectification of AC electricity to DC power is the most common and important application of a diode. A half-wave (single diode) or full-wave (four diodes) rectifier is typically used to convert AC power to DC power, especially in residential power supplies. Only half of the AC waveform travels through a diode when it receives AC power. Because this voltage pulse is utilised to charge the capacitor, it creates constant and smooth DC currents. To multiply a modest AC voltage into high DC outputs, various combinations of diodes and capacitors are utilised to produce various types of voltage multipliers.

Diodes with a Bypass

Solar panels are frequently protected by bypass diodes. Overheating occurs when the current from the other cells passes through a broken or dirty solar cell. As a result, the total output power drops, resulting in hot patches. To protect the solar cells from overheating, the diodes are connected in parallel with them. This simple setup controls the voltage across the faulty solar cell while enabling current to flow to the external circuit through intact cells.

Protection Against Voltage Surges

Most inductive loads create a high voltage when the power supply is abruptly stopped. This sudden voltage increase may cause damage to the loads. However, by attaching a diode across the inductive loads, you can protect expensive equipment. These diodes are called by a variety of names, including snubber diode, flyback diode, suppression diode, and freewheeling diode, depending on the type of security.


Transistors have changed the area of electronics as one of the most important components of an electronic circuit. These three-terminal semiconductor devices have been around for more than five decades. They’re frequently employed as amplifiers and switches. Because they can turn something “on” or “off” without moving parts, you can think of them as relays without moving parts.

A. Structure

In the beginning, germanium was utilised to make extremely temperature-sensitive transistors. They are now built of Silicon, a semiconductor substance found in sand, because Silicon transistors are significantly more temperature-tolerant and less expensive to produce. Bipolar Junction Transistors (BJT) are divided into two types: NPN and PNP. Base (b), collector (c), and emitter (e) are the three pins of each transistor (e). The layers of semiconductor material utilised to construct the transistor are referred to as NPN and PNP.

B. What Is It and How Does It Work?

An NPN transistor is created by sandwiching a p-type silicon slab between two n-type bars. One n-type is connected to the emitter, while the other is connected to the collector. The p-type is connected to the base. The excess holes in p-type silicon operate as barriers, preventing current flow. Applying a positive voltage to the base and collector while negatively charging the emitter causes electrons to flow from the emitter to the collector.

In a PNP transistor, the arrangement and quantity of p-type and n-type blocks remain inverted. One n-type is sandwiched between two p-type blocks in this sort of transistor. A PNP transistor works differently than an NPN transistor because the voltage allocation is different. A positive voltage to the base is required for an NPN transistor, whereas a negative voltage is required for a PNP transistor. To turn a PNP transistor on, the current must flow away from the base.

C. Purpose and Importance

In most electronic circuits, transistors serve as both switches and amplifiers. A transistor is frequently used as a switch by designers because, unlike a basic switch, it can transform a little current into a much bigger one. Although a simple switch can be used in a simple circuit, an advanced circuit may require variable currents at different stages.

Hearing Aid Transistors

The hearing aid is one of the most well-known applications of transistors. The sound waves are usually picked up by a small microphone in the hearing aid, which is then converted into fluctuating electrical pulses or currents. These currents are magnified when they pass through a transistor. The amplified pulses are then sent through a speaker, where they are converted back into sound waves. As a result, you might hear a much louder version of the ambient sounds.

Computers and Calculators with Transistors

We all know that computers use the binary language of “zero” and “one” to store and process data. Most people are unaware, however, that transistors play a crucial part in the creation of logic gates, which are the backbones of computer programmes. Transistors are frequently used with logic gates to create a unique configuration known as a flip-flop. Even after the base current is removed from this setup, the transistor stays “on.” When new current passes through it, it now turns on or off. As a result, a transistor may hold a zero when it’s turned off or a one when it’s turned on, which is how computers work.

Darlington Transistors are a type of transistor.

Two PNP or NPN polar junction transistors are combined to form a Darlington transistor. It bears the name of its creator, Sidney Darlington. A Darlington transistor’s main purpose is to deliver a large current gain from a low base current. These transistors can be found in power regulators, display drivers, motor controllers, light and touch sensors, alarm systems, and audio amplifiers, among other instruments that require a high current gain at a low frequency.

MOSFET and IGBT Transistors

Insulated-Gate Bipolar Transistor (IGBT) transistors are commonly employed as amplifiers and switches in a wide range of devices, including electric cars, trains, refrigerators, air conditioners, and even stereo systems. Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs), on the other hand, are frequently employed in integrated circuits to manage a device’s power levels or to store data.


A resistor is a two-terminal passive electrical device that opposes current flow. It is most likely the most basic component in an electrical circuit. Resistance is present in practically all electronic circuits, making it one of the most prevalent components. Typically, they are color-coded.

A. Structure

Because resistance is a natural feature of practically all conductors, a resistor isn’t a complicated gadget at all. A capacitor is made out of a copper wire that is wrapped around an insulating material like a ceramic rod. The resistance is proportional to the number of turns and the thickness of copper wire. The resistance increases as the number of turns and wire thickness increase.

Resistors built of a spiral pattern of carbon film are also available. Carbon film resistors get their name from this. Carbon film resistors are not as exact as wire-wound competitors, thus they’re best for low-power circuits. They are, nonetheless, less expensive than connected resistors. Both ends of the wire are connected with wire terminals. The electricity can flow in either direction via resistors since they are blind to the polarity in a circuit. As a result, there’s no need to be concerned about whether they’re attached front or backward.

B. What Is It and How Does It Work?

A resistor may appear to be insignificant. It may appear like it does nothing but devour energy. It does, however, serve an important purpose: it regulates the voltage and current in your circuit. Resistors, in other terms, allow you control over the layout of your circuit.

When an electric current is applied to a wire, all of the electrons begin to move in the same direction. It’s the same as water running through a pipe. Because there is less room for water to go through a thin pipe, less water will flow through it.

When current travels through a small wire in a resistor, the electrons find it increasingly difficult to wiggle through it. In other words, as the length and thinness of the wire grows, the quantity of electrons flowing through the resistor decreases.

C. Purpose and Importance

The three most typical applications for resistors are regulating current flow, splitting voltage, and resistor-capacitor networks.

Controlling Current Flow

Current will flow at dangerously high levels if resistors are not added to a circuit. It has the potential to overheat and damage other components. An LED, for example, might be connected directly to a battery and still function. However, after a while, the LED will become as hot as a fireball. Because LEDs are less heat tolerant, it will eventually burn.

However, if you add a resistor to the circuit, the current flow will be reduced to an optimal amount. As a result, you can leave the LED on for longer without it overheating.

Voltage Division

To lower the voltage to the required level, resistors are also utilised. A specific component in a circuit, such as a microcontroller, may require a lower voltage than the circuit as a whole. A resistor is used in this situation.

Assume your circuit is powered by a 12V battery. The microcontroller, on the other hand, simply requires a 6V supply. To divide the voltage in half, simply connect two resistors with the same resistance value in series. The cable connecting the two resistors has cut the voltage of the circuit where the microcontroller can be connected in half. You can lower the voltage in the circuit to any level by using appropriate resistors.

Networks of Resistor-Capacitor

Resistors and capacitors are also used together to make ICs with resistor-capacitor arrays on a single chip. RC filters and RC networks are other names for them. They are frequently used to suppress electromagnetic interference (EMI) or radio frequency interference (RFI) in a variety of instruments, including computer and laptop input/output ports, LANs, and WANs, among others. Machine tools, switchgears, motor controllers, automated equipment, industrial appliances, elevators, and escalators are all places where they’re utilised.