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Tuesday, February 17, 2009

Experiment: Study of Diode Characteristics

Theory: -
A p-n junction is a two-terminal device that acts as a one-way conductor. When a diode is forward biased as shown in Figure1 (a), Current flows through the diode and current is given by

ID = IS (e Vo/nVT – 1) ------ (1)

When, n is the ideality factor and 1 ≥ n ≥ 2. IS is the reverse-saturation current and VT = KT/ q is the thermal voltage. VT is about 0.026V at room temperature.

When it is reverse biased as shown in Figure, ID = - IS. As it is generally in PA (Pico-Amp) range, in many applications this current is neglected and diode is considered open

ID = IS (e –VR/VT - 1) = - IS for | V | >> VT ------- (2)

The material for p-n junction diode is silicon semiconductor. Semiconductors are a group of materials having electrical conductivity intermediate between metals and insulators. Metals: Al (Aluminum), Cu (Copper), Au (gold), Insulators: Ceramic, Wood, Rubber. Semiconductor: Si (Silicon), Ge (Germanium), GaAs (Gallium-Arsenide).

Apparatuses: -

· p-n junction diode (1N4003) ---- 1 Piece

· 5V Zener Diode ------------------- 1 Piece

· Resistor (1K) ---------------------- 1 Piece

· DC Power Supply ---------------- 1 Piece

· Signal Generator ----------------- 1 Piece

· Oscilloscope ---------------------- 1 Piece

· Chords and Wire ----------------- Lot

Data Table of Forward Region: -

VS (Volt)

VR

VD (Volt)

ID (mA)

0.1

0

0.16

0

0.5

0.12

0.46

0.12

0.7

0.24

0.5

0.24

1.0

0.5

0.53

0.5

1.5

1.0

0.36

1.0

2.0

1.5

0.6

1.5

2.5

2.0

0.6

2.0

3.0

2.5

0.61

2.5

3.5

3.0

0.62

3.0

4.0

3.5

0.63

3.5

4.5

4.0

0.63

4.0

5.0

4.5

0.63

4.5

Data Table of Reverse Region: -

(Volt)

VR

VD (Volt)

ID (mA)

0.1

0

0.15

0

0.3

0

0.34

0

0.5

0

0.54

0

0.7

0

0.72

0

1.0

0

1.03

0

2.0

0

2.05

0

3.0

0

3.11

0

4.0

0

4.06

0

5.0

0.04

5.05

0.04

6.0

0.52

5.56

0.52



















Procedure: -
  1. Measure resistance accurately using multimeter. Construct the circuit as shown in Figure- 2. Vary input voltage (Vdc) and measure VD, VR for values of VD = 0.1V, 0.2V, 0.3V, 0.4V, 0.5V, 0.6V, 0.7V and so on. Obtain maximum value of VD without increasing Vdc beyond 25V (Note that ID = VR/R).
  2. Repeat step-1 for the values at VZ = 0.5V, 1.0V, 1.5V, 2.0V, 2.5V, 3.0V and so on up to the maximum value obtainable without increasing Vdc beyond 25V. Apply circuit in Figure-3 for this step.
  3. Construct the circuit as shown in the Figure-4. Set the oscilloscope in X-Y mode and locate the zero point on oscilloscope display. Make proper connection (according to Figure-4) and observe the output.
  4. Repeat step-3 by increasing supply frequency to 5 KHz.























Report: -

  1. Plot diode I-V chrematistics for different reading obtained in this experiment.
  2. Explain the result obtained in Figure-1, 2, 3, 4.

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