What is the typical forward voltage drop across a silicon diode?

• A. 0.2 V
• B. 0.7 V
• C. 1.2 V
• D. 2.0 V

Answer: (B)

Forward bias on a silicon diode requires about 0.6 to 0.7 volts to turn on at typical operating currents. This 0.7 V drop is a convenient rule of thumb used in circuit design because, once the junction conducts, the voltage across the diode stabilizes around that value. The exact drop depends on current and temperature—the forward voltage rises slightly as current increases, so you might see around 0.8–1.0 V at higher currents. Values as low as 0.2 V aren’t typical for silicon diodes under normal forward conduction (they would point to a different device type or very small current), while 1.2 V or 2.0 V would require unusually high currents or special conditions. Therefore, about 0.7 V best matches the common silicon diode forward drop.