JNTU B.Tech III BASIC ELECTRONICS Previous Question Paper (March - 2021 - R13)

A p-n junction diode is formed by joining p-type and n-type semiconductors, creating a depletion region at the interface due to the diffusion of majority carriers. This region contains immobile ions, creating a built-in potential barrier.

In forward bias, the p-side is connected to the positive terminal and the n-side to the negative terminal. This reduces the depletion width and the potential barrier, allowing majority carriers to cross the junction, resulting in an exponential increase in current once the cut-in voltage (approx. 0.7V for Silicon) is exceeded.

In reverse bias, the p-side is connected to the negative terminal and the n-side to the positive terminal. This widens the depletion region and increases the potential barrier, preventing majority carrier flow. A very small reverse saturation current flows due to thermally generated minority carriers, which remains nearly constant until the breakdown voltage is reached.

For a Full Wave Rectifier without a filter, the ripple factor is defined as the ratio of the RMS value of the AC component to the DC component of the output voltage. The output voltage is V(t) = Vm sin(ωt). The RMS value is V(rms) = Vm / sqrt(2) and the DC value is V(dc) = 2Vm / π. The ripple factor is calculated as:

With a capacitive filter, the capacitor charges to the peak voltage and discharges through the load during the off-cycle. Assuming a large capacitor where the ripple is small, the peak-to-peak ripple voltage is V(r) = Vm / (2fCR). The ripple factor is given by:

This shows that the ripple factor is inversely proportional to the capacitance and load resistance, significantly reducing the AC content compared to the unfiltered output.