GopalKrishna Advanced Rural Research Foundation
GARRF Virtual Engineering & Electronics Laboratory
KALAM ZERO RESEARCH FUNDING LAB
EXPERIMENT 05
PN JUNCTION DIODE
V-I CHARACTERISTICS
VIRTUAL LAB
KALAM ZERO RESEARCH FUNDING LAB
A semiconductor diode is a fundamental electronic component that allows current to flow predominantly in one direction. In this experiment, students investigate the relationship between applied voltage and diode current.
To study the forward and reverse V–I characteristics of a PN junction diode and determine its approximate cut-in voltage and dynamic behaviour.
Predict what will happen before moving the voltage slider. Ask yourself:
A PN junction diode is formed by joining P-type and N-type semiconductor materials. The junction creates a depletion region and an internal potential barrier.
In forward bias, the P-side is connected to the positive terminal and the N-side to the negative terminal of the source. As the applied voltage increases, the depletion barrier is reduced and current increases rapidly.
In reverse bias, the P-side is connected to the negative terminal and the N-side to the positive terminal. Only a very small reverse saturation current flows until breakdown conditions are approached.
where IS is the reverse saturation current, n is the ideality factor and VT is the thermal voltage.
For a practical silicon diode, significant forward conduction typically begins around the region of approximately 0.6–0.7 V. The exact value depends on the device, current and temperature.
The numerical values update live as the applied voltage changes. During an automatic scan, each new measurement is immediately plotted on the V–I graph.
Horizontal axis: diode voltage. Vertical axis: diode current. The forward characteristic rises sharply after the knee region.
Pause the experiment at selected voltages and record the corresponding current.
| Trial | Bias | Diode | R | Voltage | Current |
|---|
Confused about forward bias, reverse bias or the diode characteristic? Ask CHITTI for help.
"Why does a diode conduct in one direction?"
"What is the depletion region?"
"Why is silicon diode knee voltage around 0.7 V?"
"What is reverse saturation current?"
"What is the difference between silicon and germanium?"
If the series resistance is increased, what will happen to the current for the same applied voltage? Try predicting the answer before changing R.
In a real laboratory, a current-limiting resistor should always be used with a diode to prevent excessive current. Do not connect a practical diode directly across an unlimited voltage source.