Diode

A diode is an electronic component that allows current to flow in only one direction and exhibits much higher resistance in the opposite direction. electricity The most commonly used type of diode in circuit design, due to its practicality and low cost, is the semiconductor diode. Modern common

Principle of Diode Operation

When a diode is connected in a battery-lamp circuit, it either permits or blocks current flow to the lamp depending on the polarity of the applied voltage.

1. Forward-Biased Diode: In forward bias, the diode conducts current. The depletion region formed at the P-N junction narrows when voltage is applied, resulting in lower resistance to current flow. In this state, the voltage drop across the diode remains approximately constant, typically around 0.7 V for silicon diodes and 0.3 V for germanium diodes.

2. Reverse-Biased Diode: In reverse bias, the diode blocks current flow. The depletion region at the P-N junction widens further, making it difficult for current to pass. In this condition, the current flowing through the diode is very small and is referred to as leakage current.

Forward and reverse biased diode.

Diode Symbol and Current Direction

The diode symbol is typically represented by a triangle with a line at its base. The tip of the triangle indicates the conventional current direction, from anode to cathode. If we consider electron flow, the direction of current is opposite, so electron flow runs counter to the arrow in the symbol.

The behavior of a diode can be compared to a control valve used in fluid systems. A control valve allows flow in only one direction while blocking it in the opposite direction, similar to the behavior of a diode in reverse bias.

Diode Symbol.

Forward Voltage and Current Relationship of Diodes

When forward voltage is applied, a relatively small voltage drop occurs across the diode. For silicon diodes, this drop is approximately 0.7 V, and for germanium diodes, it is about 0.3 V. Diodes operate based on this fixed voltage drop, which enables their use in rectifier applications.

The relationship between voltage and current across a diode is described by the diode equation. This equation accounts for the current flowing through the diode, the voltage drop, temperature, and certain physical constants. However, when analyzing simple diode circuits, the forward voltage drop is commonly assumed to be a constant value—0.7 V for silicon and 0.3 V for germanium.

Diode Equation.

Reverse Voltage (PIV) and Diode Breakdown

Reverse-biased diodes may experience breakdown under high reverse voltage. When a diode exceeds a certain reverse voltage threshold, breakdown occurs and the diode begins to conduct in the reverse direction. This maximum reverse voltage value is called PIV (Peak Inverse Voltage) and is typically specified by the manufacturer. Silicon diodes generally have PIV ratings above 50 V.

Diodes are critical components in modern electronic circuits. Due to their ability to conduct current in forward bias and block it in reverse bias, they are widely used in rectification, signal processing, and protection circuits. Key characteristics of diodes include forward voltage drop, PIV rating under reverse voltage, and leakage current.