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This laboratory report details an experiment on diode characteristics, focusing on the forward and reverse bias conditions of a pn junction diode. The report includes a detailed procedure, data tables, graphs, and observations, providing a comprehensive understanding of diode behavior. The experiment aims to analyze the relationship between voltage and current in both forward and reverse bias modes, demonstrating the diode's ability to conduct current in one direction and block it in the other. The report concludes with a summary of the findings and their implications for understanding diode operation.
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Southern Luzon State University College of Engineering Lucban, Quezon ECE01aL – Electronics Circuits, Analysis and Design Laboratory LABORATORY # DIODE CHARACTERISTICS Group No: 16 ARTILLAGA, Clarisse Ann BALDOVINO, Neil Schumacher D. CABALSA, Irish Nicole S. CARILLO, Miguel Andrei GAMITIN, Raiver D. BSEE II GJ Date of Performance: February 28, 2025 Date of Submission: March 14, 2025 RATING
To plot forward and reverse characteristics of a given PN junction diode. II. INTRODUCTION Semiconductors, like Silicon or Germanium, are elements having resistivity that are intermediate between a conductor and an insulator. They inherently have four electrons in the valence band which helps them to form covalent bonds with four neighboring silicon atoms. Hence, at absolute zero, the material behaves like an insulator. At room temperature, few of these electrons absorb enough energy to break away from the nucleus and serve as conduction electrons. The conduction properties can also be easily changed by changing the doping (adding different elements to) the semiconductor. Addition of a pentavalent impurity such as Phosphorus, N – type dopant, gives an additional electron after the four silicon bonds are satisfied. Similarly, a trivalent impurity such as Boron, P‐type dopant, creates an absence of electron, a hole. The entire semiconductor material is a single crystal, with one region dopes to be P‐type, with excess holes, and the adjacent region to be N‐ type, with excess electrons. This creates a metallurgical junction between the p and n regions. The contact to the p region is called the anode and that of the n region is called cathode. Equilibrium P – N junction A large density gradient in both hole and electron concentrations occur at this junction. Initially, then, there is a diffusion of holes from the p region to the n region and diffusion of electrons from n region to the p region. The flow of holes from p region uncovers negatively charged acceptor ions, and the flow of electrons uncovers positively charged donor ions. This action creates a charge separation which sets up an electric field oriented in the direction from the positive to the negative charge. This sets up an electric field in such a direction as to oppose the movement of electrons and holes eventually. The region surrounding the junction which contains immobile charges is called the “space charge” or “depletion” region. The electric field creates a potential difference across the region, which is called the built‐in potential barrier. This is about 0.7 V for a Si diode at room temperature. Forward Biased P N junction Application of a positive voltage to the p region and negative voltage to the n region creates an additional electric field in the space charge region. But this time the field opposes the space – charge E‐field. This disturbs the balance between diffusion and E‐field force. Hence majority carriers from the p region diffuse over to the n side and electrons from n side move over to the p side of the junction. This process continues if the voltage is applied. Thus, in the forward bias mode, the diode carries a large current. Reverse Biased P N junction A voltage source with its positive terminal connected to the n region and negative terminal connected to the p region reverse biases the P‐N junction. This increased electric filed holds back the holes in the p region and electrons in the n region and hence, there is no current flow. The electric field and the width of the space‐charge region increases. There is also a decrease in junction capacitance associated due to increase in the width. Thus, the reverse bias region is characterized by negligible current (due to minority carriers) even on the application of a very high voltage across the terminals, the limit being decided by reverse breakdown voltage of the diode. III. EQUIPMENT
Obtaining Results and Interpreting them: IV. DATA & RESULTS/ILLUSTRATION Forward Biased P‐N junction Sr. No. Supply Voltage (V)
mV VR (V) ID (mA) 1.28 0.5863 0. 6950 0.
For the activity regarding diode characteristics, first, we are tasked to get the things that will be needed in the laboratory experiment. The given voltage supply that was given to us has the highest value of 13 V and lowest value of 1.28 V. Then we created the circuit in the breadboard and started measuring the supply voltage, the voltage across the resistor, and the current flowing in the diode. We had enjoyed twisting the device to supply the exact voltage. For the forward biased, we noticed that the value for the voltage across the resistor increases as the supply voltage increases. On the other hand, the current flowing at the diode also increases as the value of the voltage supply also increases. For the reverse biased, we measured the values by exchanging the polarity of the supply. For the voltage across the resistor and the current across the diode, we observed that the values for both of these are all zeroes or if not, there is a very small amount that is already not significant. VII. CONCLUSION In this experiment, we studied the forward and reverse characteristics of a PN junction diode. Our goal was to observe how the voltage and current change under different biasing conditions. For the forward bias, as we increased the supply voltage, the voltage across the resistor and the current through the diode both increased. This is typical behavior for diodes, as current starts to flow more easily once the forward voltage threshold (around 0.7 V) is reached. The results showed a clear increase in current as the supply voltage increased, confirming the expected behavior of the diode in forward bias. In the reverse bias condition, the diode effectively blocked the current flow, as we observed that the current remained almost zero regardless of the increase in supply voltage. The voltage across the resistor was also very small or zero, which demonstrates that the diode prevents current from flowing in the reverse direction. Overall, the experiment confirmed the expected characteristics of a PN junction diode: it allows current to flow in the forward direction and blocks current in the reverse direction. The data from both forward and reverse bias conditions matched theoretical predictions, providing us with a clear understanding of the diode's behavior.
