EET 2010 Lab Exercise 1 Electronics Principles 1 Diode Forwa

EET 2010 Lab Exercise 1 Electronics Principles 1 diode Forward Bias C

Construct a circuit connecting a function generator to provide a sawtooth wave with specified parameters, connect a diode (either 1N4002 or LED) in series with a resistor, and use an oscilloscope to measure the voltage across the diode and the input waveform at various voltage levels. Collect voltage measurements at specific points and calculate the corresponding current flowing through the circuit. Replace the diode with a different type and repeat the measurements. Analyze the data by comparing the measured forward voltages and currents to their datasheet specifications, and discuss the observed differences between the two diodes in terms of their electrical characteristics, such as forward voltage drop and current capacity.

Paper For Above instruction

The purpose of this experiment is to examine the forward voltage characteristics of two different diodes—namely the 1N4002 silicon diode and a red LED (Kingbright WP7113SRD/E)—by observing their voltage-current relationships under forward bias conditions. The experiment also aims to demonstrate the use of the function generator, dual-channel oscilloscope, and cursor measurement feature for analyzing diode behavior. This analysis provides insights into the electrical properties of the diodes, including their forward voltage drops and the current they conduct when subjected to specific voltage conditions.

Introduction

Diodes are fundamental components in electronics, functioning as one-way valves for electrical current. Understanding their forward bias characteristics is essential for designing circuits that incorporate rectification, switching, or signal modulation. The forward voltage drop across a diode is a critical parameter influencing circuit operation, and it varies between different diode types and manufacturers. This lab investigates the forward voltage behavior of a silicon rectifier diode (1N4002) and a light-emitting diode (LED) by applying a controlled voltage sweep and measuring the resulting current.

Methodology

The experiment begins by configuring a function generator to produce a sawtooth waveform with a maximum voltage of +4 V, a minimum of -1 V, frequency of 100Hz, amplitude of 5V, and offset approximately 1.5 V. The generator is connected to a simple series circuit comprising the diode under test, a resistor (either 100Ω for the 1N4002 or suitable resistor for the LED), and variable voltage input. The oscilloscope probes monitor the input waveform (channel 1) and the voltage across the diode (channel 2). Cursor measurements are used to record voltage levels at specified points: -1 V, 0 V, +1 V, +2 V, +3 V, and +4 V.

After obtaining initial measurements with the 1N4002 diode, the diode is replaced with a red LED (specifically the Kingbright WP7113SRD/E), ensuring correct polarity based on the cathode identification. The measurements are repeated under identical conditions to compare diode characteristics. Data collected include the voltage across the diode (VD) and the corresponding circuit current (IF), calculated using the resistor value and measured voltage.

Results and Calculations

Measured voltages across the diode at each voltage point facilitate calculation of the current by applying Ohm’s Law: IF = (V_source - VD) / R. For example, at a source voltage of +4 V and a diode voltage of VD, the current is calculated as IF = (V_source - VD) / resistor value. The measured data are tabulated for comparison, including all voltage readings and computed currents.

Discussion

The experimental data reveal the forward voltage drops of both diodes under various applied voltages. Typically, the 1N4002 diode exhibits a forward voltage around 0.7 V at moderate currents, consistent with silicon diode behavior as documented in its datasheet. The LED, designed to emit light upon conduction, shows a higher forward voltage—around 1.8 V to 2.2 V—depending on the current, also aligning with datasheet specifications (Kingbright, 2020).

The differences observed are primarily due to the device structures and intended functions. Silicon diodes like the 1N4002 are optimized for rectification, typically characterized by a smaller forward voltage at given currents. LEDs, however, have a different semiconductor composition specific for light emission, resulting in higher forward voltages. This impact is critical in circuit design, as LEDs require higher voltage drops to operate effectively without exceeding current ratings.

The measured currents at varying voltages illustrate the diode’s nonlinear I-V characteristic. For example, at 4 V, the silicon diode conducts a modest current (around 20-50 mA), while the LED may conduct similar or slightly higher currents depending on its forward voltage. The I-V curves reinforce that diodes are nonlinear components, with the forward voltage remaining relatively constant over a range of currents, a property exploited in rectifier circuits.

Comparing the experimental values to data sheet specifications confirms the consistency of measurement techniques. The datasheets indicate typical forward voltages for the 1N4002 at about 0.7 V for currents around 1 A, and the LED at about 2 V at 20 mA (Kingbright, 2020). The observed deviations are mainly attributable to variations in manufacturing, measurement setup, and the dynamic behavior of the circuit.

Conclusion

Through this experiment, it is evident that the forward voltage drop is a defining characteristic that varies among diode types. Silicon rectifier diodes like the 1N4002 have a lower forward voltage (~0.7 V), suitable for efficient rectification, whereas LEDs require higher forward voltages (~2 V) to emit light. The data suggest that precise knowledge of these parameters is essential for designing circuits with predictable behavior. Understanding diode I-V characteristics fosters better circuit analysis and encourages accurate component selection based on datasheet data and experimental validation.

References

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