Zener Diode: 15 MCQs with answers

The reverse voltage exceeds the Zener voltage

Zener breakdown occurs in the reverse-biased region when the reverse voltage reaches the Zener voltage (V_Z), causing a sharp increase in reverse current.

Voltage regulator

Zener diodes are widely used as voltage regulators because they maintain a nearly constant voltage across them when operated in the breakdown region.

Zener voltage (V_Z)

The Zener voltage (V_Z) is the reverse breakdown voltage at which the diode starts conducting in reverse, and it is a primary specification.

Reverse bias

Zener diodes are designed to operate in the reverse breakdown region, so they are connected in reverse bias.

Acts as an open circuit

Below the Zener voltage, the reverse current is very small (microamperes), so the diode behaves almost like an open circuit.

False

A Zener diode regulates voltage when operated in the reverse breakdown region, not in forward bias.

True

Zener voltages are typically several volts (e.g., 3.3 V, 5.1 V), while the forward voltage drop is around 0.7 V for silicon diodes.

Nearly constant at V_Z

Once breakdown occurs, the voltage across the Zener diode remains approximately equal to its Zener voltage (V_Z) over a wide range of reverse currents.

A sharp increase in reverse current at a specific voltage

Zener breakdown results in a sharp, almost vertical increase in reverse current once the reverse voltage reaches V_Z.

Limit the current through the Zener diode

The series resistor drops the excess voltage and limits the current through the Zener diode to a safe value.

Signal amplification

Zener diodes are not used for signal amplification; they are used for voltage regulation, protection, and reference purposes.

The doping level of the diode

The Zener voltage is set by the doping concentration in the diode; heavier doping leads to lower breakdown voltages.

It indicates the maximum current the diode can handle without damage

The power rating (P_Z = V_Z * I_Z) specifies the maximum power the diode can dissipate safely; exceeding it can destroy the device.

Decreases

The total current through the series resistor is approximately constant if the input voltage is constant. When load current increases, the Zener current decreases to maintain the total current.

Zener breakdown

For low breakdown voltages (below ~5 V), the Zener effect (direct electric field ionization) dominates; above ~5 V, avalanche breakdown is more common.