Which diodes conduct current in the opposite direction after a threshold?

Which diodes conduct current in the opposite direction after a threshold?

• A. Zener diodes
• B. Diodes
• C. LEDs
• D. Photodiodes

Answer: (A)

The key idea is a device that begins to conduct in reverse once a specific voltage is reached. A Zener diode is designed for this: when the reverse voltage across it reaches its Zener voltage, it conducts in reverse in a controlled way, clamping or regulating the voltage at that level. In forward bias, it behaves like a regular diode, dropping about 0.7 V, but the distinct feature is its predictable reverse conduction at the Zener voltage, which is exactly what the question describes. Regular diodes don’t provide a reliable, defined reverse conduction threshold for regulation, LEDs are optimized for forward conduction to emit light, and photodiodes respond to light or operate in reverse bias as detectors rather than providing a stable reverse-conduction threshold for regulation.

The key idea is a device that begins to conduct in reverse once a specific voltage is reached. A Zener diode is designed for this: when the reverse voltage across it reaches its Zener voltage, it conducts in reverse in a controlled way, clamping or regulating the voltage at that level. In forward bias, it behaves like a regular diode, dropping about 0.7 V, but the distinct feature is its predictable reverse conduction at the Zener voltage, which is exactly what the question describes. Regular diodes don’t provide a reliable, defined reverse conduction threshold for regulation, LEDs are optimized for forward conduction to emit light, and photodiodes respond to light or operate in reverse bias as detectors rather than providing a stable reverse-conduction threshold for regulation.