JNTU B.Tech II Year ANALOG AND DIGITAL ELECTRONICS Previous Question Paper (March - 2022 - R18)

When a PN junction is forward biased, the positive terminal of the external battery is connected to the P-type region and the negative terminal to the N-type region. This configuration reduces the potential barrier at the junction. The holes in the P-region are repelled by the positive terminal, and electrons in the N-region are repelled by the negative terminal, forcing both charge carriers toward the depletion region.

As the forward voltage increases, the width of the depletion region decreases, allowing majority carriers to cross the junction easily. This results in a significant flow of current known as forward current. The V-I characteristics show that the current increases exponentially with the applied voltage once it exceeds the cut-in voltage (approximately 0.3V for Germanium and 0.7V for Silicon). Below this threshold, the current is negligible.

A Half Wave Rectifier uses a single diode in series with the load. During the positive half cycle of the AC input, the diode is forward biased and conducts, allowing current to flow through the load. During the negative half cycle, the diode is reverse biased, acting as an open circuit, resulting in zero output current. This produces a pulsating DC output with high ripple content.

Without a filter, the output is a series of positive half-sine pulses. The efficiency is low (approximately 40.6%) and the ripple factor is high (1.21).

With a filter, such as a capacitor placed in parallel with the load, the output is smoothed. During the conduction period, the capacitor charges to the peak value of the input voltage. During the non-conduction period (when the diode is reverse biased), the capacitor discharges through the load, maintaining a more constant voltage level. This significantly reduces the ripple content and provides a more stable DC output.