FCC Exam Question: 3-5A3

MOSFETs are manufactured with THIS protective device built into their gate to protect the device from static charges and excessive voltages:

A. Schottky diode.
B. Metal oxide varistor (MOV).
C. Zener diode.
D. Tunnel diode.
Correct Answer: C

Explanation: MOSFET gates are incredibly sensitive to static electricity and excessive voltages due to their very high input impedance and thin insulating oxide layer. Even a small static charge can generate enough voltage to puncture and permanently damage this delicate gate oxide. **Zener diodes** are specifically designed to break down and conduct current at a precise reverse voltage (the Zener voltage). By integrating a Zener diode (or a pair of back-to-back Zeners) directly into the MOSFET gate input, any voltage exceeding the Zener voltage is safely shunted away from the gate to ground, protecting the device. **Schottky diodes** are known for their fast switching and low forward voltage drop, used in rectification and switching, but not for precise voltage clamping in this protective manner. **Metal oxide varistors (MOVs)** are discrete components used for larger surge protection in power circuits, not integrated into sensitive gates. **Tunnel diodes** exhibit negative resistance and are used in high-frequency oscillators, unrelated to overvoltage protection.

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Includes Elements 1, 3, 6, 7R, 8, and 9.