2. THEORY
PN Junction Diode
A PN-junction diode is formed when a p-type semiconductor is fused to an n-type semiconductor. A PN junction diode has the characteristic of passing current in only one direction.
Characteristics of Diode
a. Reverse Bias: When a diode is connected to a battery as shown, holes in the n-side are forced to the left while electrons in the p-side are forced to the right. This results in an empty zone around the pn-junction that is free of charge carriers, creating a depletion region. This depletion region acts as an insulator, preventing current from flowing through the diode. When a diode is arranged in this way, it is said to be reverse-biased.
b. Forward Bias: When a diode is connected to a battery as shown, electrons from the n-side and holes from the p-side are forced toward the center by the electrical field supplied by the battery. The electrons and holes combine, causing the current to pass through the diode. When a diode is arranged in this way, it is said to be forward-biased.
Zener Diode
A Zener diode is a heavily doped semiconductor diode designed to operate specifically in the breakdown region. When the diode current is greater than the knee current (Izk), the voltage across the Zener diode remains almost constant, independent of the reverse current that is flowing through it. This property is used to regulate the voltage.
Rectifier
A device capable of converting an AC signal into a signal with a DC component is called a rectifier. Rectifiers are generally classified into half-wave and full-wave rectifiers.
a. Half-wave rectifier: The transformer steps down the main voltage, and the diode conducts only during the positive half-cycle of the secondary winding. This results in a pulsating DC voltage across the load.
b. Bridge full-wave rectifier: For the positive half-cycle of the secondary voltage, diodes D1 and D2 conduct. For the negative half-cycle, diodes D3 and D4 conduct, resulting in a rectified voltage across the load for both half-cycles.
5. DISCUSSIONS
Firstly, we investigated the PN junction diode characteristics. We observed that the forward bias condition allows current to flow, while the reverse bias condition results in very little current flow until breakdown. In the lab, we were unable to observe reverse breakdown because the source voltage was always greater than 1V, while the breakdown is less than 0.7V.
A Zener diode works in the reverse biasing mode. Due to a lack of instruments, we were unable to observe the reverse characteristic of the diode.
In contrast, the full-wave rectifier circuit rectifies both halves of the AC waveform, resulting in a smoother DC output compared to the half-wave rectifier, which is simple but inefficient. In the lab, we supplied 24.8 V AC and got 11.1 V DC as output in half-wave rectification. Similarly, we supplied 24.8 V AC and got 21.7 V DC as output in full-wave rectification.
6. CONCLUSION
Hence, the characteristics of PN and Zener diodes were observed, and both half-wave and full-wave rectifiers were studied in the experiment.
