What is the function of a diode in a circuit?

• A. Allows current to flow in one direction and blocks the opposite
• B. Stores energy
• C. Increases current
• D. Generates voltage

Answer: (A)

A diode acts as a one-way valve for electrical current. It conducts when the anode is more positive than the cathode (forward bias) and blocks current when the polarity is reversed (reverse bias). In forward bias, a small threshold voltage is needed before it starts conducting (about 0.7 V for silicon), after which current can flow through the diode. In reverse bias, the current is minimal until a breakdown occurs. This unidirectional behavior is why diodes are used for rectifying AC to DC, protecting circuits from reverse polarity, and demodulating signals. A device that stores energy isn’t a diode (that’s a capacitor or inductor), one that increases current isn’t the diode’s job, and one that generates voltage is a power source; the diode’s function is simply to permit current in one direction and block it in the other.