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.

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