Experiment 9 : To draw the I-V characteristic curve for a p-n junction diode in forward and reverse bias.

Experiment 9 : To draw the I-V characteristic curve for a p-n junction diode in forward and reverse bias.

Experiment 9 : I-V Characteristics of a P-N Junction Diode in Forward and Reverse Bias 

Aim:

To study and plot the current-voltage (I-V) characteristics of a p-n junction diode under forward bias and reverse bias conditions.

Apparatus Required:

  • P-N junction diode
  • DC regulated power supply
  • Resistor (1 kΩ)
  • Voltmeter (0–2V range)
  • Ammeter (0–100mA for forward bias, 0–1mA for reverse bias)
  • Breadboard or connecting wires

Theory:

A p-n junction diode allows current to pass primarily in one direction. It acts as a rectifier, blocking current in the reverse direction.

Forward Bias:

In forward bias, the p-side is connected to the positive terminal and the n-side to the negative terminal of the power supply. This reduces the potential barrier and allows significant current flow once the forward voltage exceeds a certain threshold (~0.7V for silicon).

Reverse Bias:

In reverse bias, the p-side is connected to the negative terminal and the n-side to the positive. This increases the barrier, and only a small leakage current (reverse saturation current) flows.

Circuit Diagrams:

Forward Bias:

I-V Characteristics of a P-N Junction Diode (Forward and Reverse Bias)


Reverse Bias:

I-V Characteristics of a P-N Junction Diode (Forward and Reverse Bias)


Procedure:

  1. Connect the circuit in forward bias mode using the diode, resistor, ammeter, and voltmeter.
  2. Gradually increase the input voltage in steps (e.g., 0.1V) and record the corresponding current values.
  3. Note the voltage at which current increases sharply—this is the "knee voltage."
  4. Now reverse the diode and repeat the experiment in reverse bias mode.
  5. Record the leakage current values for increasing reverse voltage.

Observation: 

1. Table for forward-bias voltage and forward current

Serial No. of Obs. (1) Forward-bias Voltage VF (V) (2) Forward current IF (mA) (3)
1. 0 0
2. 0.1 0
3. 0.2 0
4. 0.3 0
5. 0.4 0.5
6. 0.6 1
7. 0.8 2
8. 1.0 3
9. 1.2 5
10. 1.4 7.5
11. 1.6 10
12. 1.8 15
13. 2.0 20
14. 2.2 25
15. 2.4 30

2. Table for reverse-bias voltage and reverse current

Serial No. of Obs. (1) Reverse-bias Voltage VR (V) (2) Reverse current IR (µA) (3)
1. 0 0
2. 5.0 1
3. 7.0 2
4. 9.0 3
5. 11.0 4
6. 13.0 5
7. 15.0 7
8. 17.0 9
9. 19.0 11
10. 21.0 13
11. 23.0 18
12. 25.0 25

Graph: Plot two graphs

Forward bias: Voltage (X-axis) vs Current (Y-axis) showing exponential rise after.

To draw the I-V characteristic curve for a p-n junction diode in forward and reverse bias.

Reverse bias: Voltage (X-axis) vs Current (Y-axis) showing nearly flat line with very small current.

To draw the I-V characteristic curve for a p-n junction diode in forward and reverse bias.

Result:

Junction Resistance for Forward bias : $40ohms$

Junction Resistance for Reverse bias : $2 \times 10^{6}$ohms

Precaution: 

  • Ensure correct polarity when connecting the diode.
  • Use proper voltage ranges to avoid diode damage.
  • Check for zero error in meters before recording readings.
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