How is Ohm's Law used in determining the voltage drop across diodes in forward bias?
1 Answer
Ohm's Law is not directly used to determine the voltage drop across diodes in forward bias. Instead, Ohm's Law is typically applied to calculate the current flowing through the diode when it is in forward bias, and from there, the voltage drop across the diode can be determined.
In forward bias, a diode allows current to flow through it, and its behavior can be approximated by a simple model using Ohm's Law. The relationship between voltage, current, and resistance is given by Ohm's Law as:
V = I * R
Where:
V = Voltage across the component (in volts)
I = Current flowing through the component (in amperes)
R = Resistance of the component (in ohms)
However, diodes do not have a fixed resistance like typical resistors. Instead, their current-voltage relationship is exponential. The Shockley diode equation models this behavior and relates the current through a diode to the voltage across it:
I = Iā * (e^(V / (n * Vt)) - 1)
Where:
I = Diode current (in amperes)
Iā = Reverse saturation current (a constant for a given diode)
V = Diode voltage (in volts)
n = Ideality factor (an empirical factor typically around 1 to 2)
Vt = Thermal voltage (k * T / q, where k is Boltzmann's constant, T is temperature in Kelvin, and q is the charge of an electron)
When a diode is in forward bias, it is typically safe to neglect the -1 term in the equation as it is much smaller than the exponential term. Thus, the equation becomes:
I ā Iā * e^(V / (n * Vt))
To determine the voltage drop across the diode in forward bias, you can use the diode equation and algebraically solve for V:
V ā n * Vt * ln(I / Iā)
Where ln denotes the natural logarithm.
Keep in mind that the diode equation is an approximation and doesn't account for all variations and complexities in diode behavior, especially at very low or high currents. Nonetheless, it is a commonly used and effective model for most practical diode applications. More accurate models and specifications can be found in the datasheets provided by diode manufacturers.
In forward bias, a diode allows current to flow through it, and its behavior can be approximated by a simple model using Ohm's Law. The relationship between voltage, current, and resistance is given by Ohm's Law as:
V = I * R
Where:
V = Voltage across the component (in volts)
I = Current flowing through the component (in amperes)
R = Resistance of the component (in ohms)
However, diodes do not have a fixed resistance like typical resistors. Instead, their current-voltage relationship is exponential. The Shockley diode equation models this behavior and relates the current through a diode to the voltage across it:
I = Iā * (e^(V / (n * Vt)) - 1)
Where:
I = Diode current (in amperes)
Iā = Reverse saturation current (a constant for a given diode)
V = Diode voltage (in volts)
n = Ideality factor (an empirical factor typically around 1 to 2)
Vt = Thermal voltage (k * T / q, where k is Boltzmann's constant, T is temperature in Kelvin, and q is the charge of an electron)
When a diode is in forward bias, it is typically safe to neglect the -1 term in the equation as it is much smaller than the exponential term. Thus, the equation becomes:
I ā Iā * e^(V / (n * Vt))
To determine the voltage drop across the diode in forward bias, you can use the diode equation and algebraically solve for V:
V ā n * Vt * ln(I / Iā)
Where ln denotes the natural logarithm.
Keep in mind that the diode equation is an approximation and doesn't account for all variations and complexities in diode behavior, especially at very low or high currents. Nonetheless, it is a commonly used and effective model for most practical diode applications. More accurate models and specifications can be found in the datasheets provided by diode manufacturers.