Fundamentals of Electronics | Lecture - 2A | Diode Theory

Описание: Principle and Characteristics of Diode Operation:
Diodes are fundamental semiconductor devices acting as one-way valves for electric current. Understanding their principle and characteristics is crucial for anyone involved in electronics.

Principle of Operation:

At its core, a diode is a P-N junction formed by joining p-type (excess holes) and n-type (excess electrons) semiconductor materials.

Depletion Region: When these materials are joined, electrons from the n-side diffuse into the p-side, and holes from the p-side diffuse into the n-side. This recombination creates a region around the junction devoid of free charge carriers, called the depletion region (or space-charge region), which acts as an insulating barrier with an inherent potential barrier (approximately 0.7V for silicon, 0.3V for germanium).

Forward Bias: When a positive voltage is applied to the p-type material (anode) and a negative voltage to the n-type material (cathode), the diode is forward-biased. If the applied voltage exceeds the potential barrier (cut-in voltage or turn-on voltage), it repels the majority carriers towards the junction, narrowing the depletion region and allowing a significant current to flow with very low resistance. The current increases exponentially after the cut-in voltage.

Reverse Bias: When a negative voltage is applied to the p-type material (anode) and a positive voltage to the n-type material (cathode), the diode is reverse-biased. This pulls the majority carriers away from the junction, widening the depletion region and significantly increasing the resistance. Ideally, no current flows, but in reality, a very small reverse saturation current (leakage current) due to minority carriers exists.

Reverse Breakdown: If the reverse voltage increases beyond a certain point, called the breakdown voltage (VBR), the diode experiences a sudden and rapid increase in reverse current. This can be destructive for standard diodes, though Zener diodes are designed to operate in this region for voltage regulation.

Key Characteristics:

Unidirectional Current Flow (Rectification): The most crucial characteristic. Diodes allow current to flow easily in the forward direction and block it in the reverse direction. This property is fundamental for rectification, converting AC to DC.

Non-Linear I-V Curve: Unlike resistors, a diode's current-voltage relationship is highly non-linear, as depicted by its characteristic curve.

Cut-in Voltage (Threshold Voltage/Turn-on Voltage): The minimum forward voltage required for the diode to begin conducting significantly.

Reverse Saturation Current: A tiny leakage current that flows in reverse bias.

Breakdown Voltage: The reverse voltage at which the diode's insulating properties break down, leading to a large reverse current.

Power Dissipation: Diodes dissipate power in the form of heat, especially in forward bias.

Important Search Queries in this Topic:

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