11.5 : Modeling of Diode Forward Characteristics

Understanding the behavior of diodes when forward-biased is a fundamental aspect of electronic circuit design and analysis. This analysis primarily utilizes two models: the exponential diode model and the constant-voltage-drop model. The exponential model comes into play when the source voltage exceeds 0.5 volts, pushing the diode current to rise exponentially above the saturation current. This relationship is graphically depicted in the current-voltage (I-V) curve, illustrating the diode's nonlinear response to increased forward voltage.

Kirchhoff's Voltage Law (KVL) facilitates deriving a mathematical expression that correlates the diode current, source voltage, and voltage drop across the diode.

The operational point of the diode, known as point Q, is identified at the intersection of the load line and the I-V curve, indicating the diode's operating current and voltage. Alternatively, the constant-voltage-drop model simplifies the analysis by assuming a steady voltage drop across the diode, typically 0.7 volts for silicon diodes. This model aids in quickly determining the diode current by integrating this constant voltage into the KVL equation.

Each model serves its purpose; the exponential model offers a detailed analysis suitable for precise circuit design, whereas the constant-voltage-drop model provides an accessible approach for basic analyses and educational applications. Understanding these models is essential for designing and analyzing electronic circuits, enabling engineers to predict circuit behavior accurately and ensure the reliability of electronic devices.