NEET Practice Questions (MCQs) with Answers & Solutions

The zener voltage of a zener diode is primarily determined by the level of doping in the semiconductor material. By changing the doping concentration, the breakdown voltage, and hence the zener voltage, can be set to a desired value. Adjusting the input voltage or current, or connecting a resistance in series, are not methods to set the zener voltage.

To obtain a constant DC voltage from the DC unregulated output of a rectifier, a zener diode is typically used. The zener diode maintains a stable output voltage by operating in its breakdown region, thus providing voltage regulation.

Zener diodes are designed to allow current to flow in the reverse direction when a certain specified voltage (Zener voltage) is reached. This characteristic makes them ideal for use as voltage regulators, which maintain a constant output voltage despite variations in the input voltage or load conditions.

For the same density of impurity atoms, Zener voltage is higher for silicon (Si) than for germanium (Ge). This is because silicon has a wider bandgap (1.1 eV) compared to germanium (0.7 eV), and a higher breakdown voltage is achieved in silicon due to its material properties.

When a p-n junction is reverse biased, the minority carriers (electrons in the p-region and holes in the n-region) move towards the junction. This movement of minority carriers causes a small reverse saturation current to flow through the junction.

Avalanche breakdown in a semiconductor diode occurs when the reverse bias voltage across the diode exceeds a certain critical value. This high reverse voltage causes a large electric field that can accelerate free electrons to high energies, leading to collisions that generate more electron-hole pairs, thus causing a large current.

The voltage gain of common emitter amplifier $ A = \beta ( {R_L \over R_i }) ,$ A = Output Voltage/ Input Voltage

$ \beta = { \alpha \over 1 - \alpha } $ $ \therefore I_B = { I_C \over \beta } $