Diode Question with Answers for Viva Interview

What is a diode?

A diode is a type of electronic component that allows current to flow through it in only one direction. It is made up of semiconductor material, such as silicon, that is treated to have different electrical properties at each end. When a voltage is applied to a diode, the current will only flow through it in the direction determined by the orientation of the semiconductor material.

Diodes are commonly used in a variety of electronic circuits to convert alternating current (AC) to direct current (DC), as well as to protect circuits from voltage spikes and rectify signals.

List different types of diodes and briefly explain.

PN junction or standard diode

These are the most basic type of diode, and they are used to allow current to flow in only one direction (from the anode to the cathode). They are typically made of silicon or germanium, and they are used in a wide variety of applications, including rectification and voltage regulation.

Zener diodes

These are a type of diode that is designed to operate in the reverse-bias mode, allowing current to flow from the cathode to the anode. They are typically used in voltage regulation circuits, where they can provide a stable reference voltage.

Light-emitting diodes (LEDs)

These are a type of diode that emits light when a current is applied to them. They are commonly used as indicator lights, and they are also used in a wide variety of lighting applications, such as in traffic signals, displays, and backlights.

Schottky diodes

These are a type of diode that has a lower forward voltage drop and a faster switching speed than standard diodes. They are commonly used in high-speed switching applications, such as in power supplies and RF circuits.

Photodiode

A photodiode is a type of diode that is sensitive to light. It is made of semiconductor material, such as silicon, that is treated to have different electrical properties at each end. When light is absorbed by the photodiode, it causes electrons in the semiconductor material to be excited, allowing them to flow freely through the material. This flow of electrons generates a current, which can be detected and measured. Photodiodes are commonly used in a variety of applications, including light sensors, optical detectors, and even medical imaging devices.

Laser diodes

These are a type of diode that emits a very narrow, highly focused beam of light. They are commonly used in a variety of applications, including data storage, medical devices, and laser printers.

Avalanche diode

An avalanche diode is a type of diode that is designed to operate in the breakdown region, where the voltage across the diode is above its breakdown voltage. In this region, the diode allows a large current to flow, and the current flow is accompanied by a phenomenon known as “avalanche breakdown”.

Avalanche diodes are commonly used in high-voltage or high-power applications, where a standard diode would not be able to handle the voltage or current levels. They are also used in some types of radio frequency (RF) circuits, where they can help to amplify the RF signal.

One of the main advantages of avalanche diodes is their ability to handle high voltage and current levels. They are also relatively fast-acting, which makes them suitable for use in high-speed switching applications. However, they can also be relatively expensive and may not be as efficient as other types of diodes in some applications.

What is a depletion layer?

The depletion layer is a region within a PN junction diode where the concentration of mobile charge carriers such as electrons and holes is diffused away or greatly reduced and the remaining is only ionized donor or acceptor impurities. Once the depletion layer of particular width is formed then it prevents further tunneling or migration of the charge carried through the depletion layer.

What are forward-biased and reverse-biased conditions of a diode?

When a voltage is applied to a diode, the direction in which the current flows through the diode depends on the polarity of the voltage. If the voltage is applied in such a way that the positive terminal is connected to Anode and the negative terminal is connected to the Cathode. Then the width of the depletion layer will be decreased and the charge carries flow through as well as the current to flow through the diode, then the diode is said to be forward-biased. In this case, the diode will act like a conductor, allowing current to flow through it with little resistance.

On the other hand, if the voltage is applied in such a way that Positive to Cathode and Negative to Anode then it blocks current from flowing through the diode, the diode is said to be reverse-biased. In this case, the width of the depletion region further increases and the diode will act like an insulator, and very little current will flow through it. Here the applied voltage should be less than the “reverse breakdown voltage” of the diode.

What will happen if a voltage above reverse breakdown voltage is applied to a diode in reverse bias?

In reverse-biased conditions, if the reverse voltage is further increased to reverse breakdown, it can cause the diode to become damaged or even destroy it. This is because the high voltage can cause a large amount of current to flow through the diode in the reverse direction, which can generate heat and cause the diode to fail. Therefore, it is important to never apply a voltage above the rated reverse breakdown voltage to a diode in reverse-biased conditions.

What is avalanche breakdown?

Where the diode’s electrons and holes are accelerated to very high speeds, colliding with other atoms and generating more free electrons and holes. This process amplifies the current flow, allowing the diode to conduct a large amount of current.

What are the basic applications of diodes?

• DC Rectifier or Converting AC to DC: Diodes are commonly used in power supplies to convert alternating current (AC) to direct current (DC). This is done by rectifying the AC signal, which essentially means that the diode allows current to flow through it in only one direction.
• Protecting circuits from voltage spikes: Diodes can also be used to protect circuits from voltage spikes, which are sudden increases in voltage that can damage electronic components. When a voltage spike occurs, the diode will conduct the excess current away from the circuit, protecting it from damage.
• Rectifying signals: In some cases, diodes can be used to rectify an electronic signal, which means that the diode will allow only certain parts of the signal to pass through it. This can be useful for filtering out noise or for shaping the signal in a specific way.
• Detecting light: As mentioned earlier, photodiodes are a type of diode that is sensitive to light. They can be used in light sensors, optical detectors, and other applications where light needs to be detected.
• Controlling current flow: Because diodes only allow current to flow through them in one direction, they can be used to control the direction of current flow in a circuit. This can be useful for creating circuits that perform logical operations, such as AND, OR, and NOT gates.
• Clipping circuits: A clipping circuit is an electronic circuit that is used to remove or “clip” a portion of a signal. This is typically done by limiting the maximum or minimum amplitude of the signal so that any signal values that exceed the specified limit are “clipped” or cut off. Clipping circuits are commonly used in audio systems to prevent distortion, as well as in other applications where it is necessary to limit the range of a signal.
• Clamping Circuits: A clamping circuit, on the other hand, is an electronic circuit that is used to hold a signal at a specific voltage level. This is typically done by using diodes to “clamp” the signal to a fixed reference voltage. Clamping circuits are commonly used to remove DC offsets from signals, as well as to protect circuits from excessive voltage levels.

How do LEDs emit light?

LEDs emit light through a process called electroluminescence. When a voltage is applied to an LED, it causes electrons in the semiconductor material to become excited and move freely through the material. As the electrons move through the material, they collide with atoms and release energy in the form of light. The color of the light emitted by an LED depends on the type of semiconductor material used in the LED and the energy band gap of the material. Different materials will produce light of different colors, ranging from red and orange to green and blue.