What is the forward voltage drop across a silicon diode?

• A. 0.0v
• B. 5.0v
• C. 1.5v
• D. 0.7v

Answer: (D)

When a silicon diode is forward-biased, a small voltage is required to push electrons and holes across the PN junction. That forward voltage drop is about 0.6 to 0.7 volts at typical operating currents, with 0.7 V being the standard approximation. This stems from the junction’s built-in potential barrier that must be overcome for conduction to begin; once conduction starts, the drop stays around this range, increasing slightly as current grows.

0.0 V would imply an ideal diode with no drop, which isn’t how real silicon diodes behave. 5.0 V is far higher than the normal forward drop for silicon diodes and would imply excessive current or an off-design condition. 1.5 V is generally higher than the typical forward drop for standard silicon diodes except at unusually high currents or with different materials. Therefore, about 0.7 V is the correct, conventional forward drop for a silicon diode.