Diodes - What Are Diodes - PN Junction - Forward Bias - Reverse Bias - Zener Diodes

Summary

This video lecture offers a comprehensive overview of diodes, focusing on their types, construction, working principles, and applications. It explains the functioning of a PN Junction diode, including the concepts of forward and reverse bias, and the formation of depletion regions. The lecture also covers the key differences between diodes like LEDs, photodiodes, and Zener diodes, emphasizing their unique characteristics and uses. Key parameters such as resistance, capacitance, and the importance of biasing are also discussed, making it an essential guide for understanding diodes in electronic circuits.

Takeaways

• 😀 William Henry Eccles coined the term 'diode' in 1919, derived from Greek roots meaning 'two electrodes'.
• 😀 Diodes are semiconductor devices formed by doping P-type and N-type extrinsic semiconductors into pure silicon or germanium.
• 😀 The PN Junction diode is the base for many types of diodes, including LEDs, photodiodes, and Zener diodes.
• 😀 A diode has two main regions: the P region (positive) and the N region (negative), creating a junction between them.
• 😀 In forward bias, the diode allows current to flow as the voltage exceeds the junction potential (0.6V for silicon).
• 😀 In reverse bias, the diode blocks current flow, but a small leakage current may occur due to minority charge carriers.
• 😀 The Zener diode is a heavily doped PN Junction diode designed to function effectively in reverse bias with controlled breakdown voltage.
• 😀 The forward characteristics of a diode show an increase in current after the junction potential is exceeded.
• 😀 In reverse bias, an increase in voltage beyond the breakdown voltage leads to diode damage, hence it’s essential to control doping.
• 😀 Diodes have DC resistance (static) and AC resistance (dynamic), influencing their operation in rectifiers and signal processing circuits.
• 😀 Diodes exhibit two types of capacitances: diffusion capacitance (forward bias) and transition capacitance (reverse bias), both essential for circuit analysis.

Q & A

What is a diode and who coined the term 'diode'?

A diode is a semiconductor device formed by doping P and N-type extrinsic semiconductors into pure silicon or germanium. The term 'diode' was coined by William Henry Eccles in 1919, derived from the Greek roots 'dye' meaning 'two' and 'ode' meaning 'electrode'.

What are the different types of diodes mentioned in the video?

The video mentions several types of diodes, including Light Emitting Diodes (LED), Photodiodes, Zener diodes, and PN Junction diodes.

How is a PN Junction diode constructed?

A PN Junction diode is constructed by doping P-type impurities like boron on one half of a semiconductor slice and N-type impurities like phosphorous on the other half. The P-type region has holes, and the N-type region has free electrons, creating a junction.

What is the role of the depletion region in a PN Junction diode?

The depletion region is formed when free electrons from the N side combine with holes from the P side, resulting in an area devoid of free charge carriers. This region develops an electric field, known as Junction potential, which restricts the movement of charge carriers unless an external voltage is applied.

What is forward bias in a PN Junction diode?

In forward bias, the positive terminal of the battery is connected to the P side (anode) and the negative terminal to the N side (cathode). This causes electrons to move from the N side to the P side, overcoming the electric field in the depletion region and allowing current to flow from anode to cathode.

What happens when a diode is reverse biased?

In reverse bias, the positive terminal of the battery is connected to the N side (cathode) and the negative terminal to the P side (anode). This causes the depletion region to widen, preventing current from flowing. However, a small leakage current may flow due to minority charge carriers.

What are the forward and reverse characteristics of a diode?

In forward bias, once the external voltage exceeds the junction potential, the current increases rapidly. In reverse bias, a small leakage current flows until the reverse voltage reaches a critical value known as the breakdown voltage, beyond which the diode may fail.

What is the significance of Zener diodes?

Zener diodes are heavily doped PN Junction diodes designed to work in reverse bias with a controlled breakdown voltage. They are used in voltage regulator circuits to prevent breakdown and component failure.

How is dynamic resistance different from static resistance in diodes?

Dynamic resistance refers to the change in voltage with respect to the change in current during AC signal operation, while static (DC) resistance is calculated by the ratio of voltage to current when a constant DC voltage is applied.

What is the difference between diffusion capacitance and transition capacitance in diodes?

Diffusion capacitance occurs during forward bias operation due to the change in charge as free electrons move from the N side to the P side. Transition capacitance occurs during reverse bias operation when majority charge carriers move away from the junction, leading to a change in charge.