Ohm's Law is not directly applicable to determining the current through a diode in reverse bias because diodes do not obey Ohm's Law under reverse bias conditions. Ohm's Law states that the current flowing through a resistor is directly proportional to the voltage across it, with the proportionality constant being the resistance:
V = I * R
Where:
V = Voltage across the resistor
I = Current flowing through the resistor
R = Resistance of the resistor
Diodes are semiconductor devices that have nonlinear characteristics, and their behavior under forward and reverse bias conditions is different.
Under forward bias (when the anode voltage is higher than the cathode voltage), the diode conducts current and follows a simple exponential relationship between current and voltage. However, under reverse bias (when the anode voltage is lower than the cathode voltage), the diode acts as an insulator and only allows a very small reverse leakage current to pass through, typically in the nanoampere range.
This reverse leakage current can be affected by factors such as temperature, voltage, and the specific diode's properties. Instead of using Ohm's Law, reverse leakage current is typically specified in diode datasheets under different reverse bias voltages.
In summary, Ohm's Law is not used to determine the current through a diode in reverse bias because the diode's behavior in reverse bias is not linear and cannot be described by a simple resistor-like relationship. Instead, manufacturers provide reverse leakage current values in the datasheet, and designers must consider this parameter in their circuit calculations to ensure proper functionality and avoid any unexpected behavior.