Experiment 3: V-I Characteristics of Silicon Semiconductor Diode

Objective:-

1.      Design the circuit diagram

2.      Draw the characteristics curve

3.      Determine the DC forward resistance.

Equipments required:-  

1.    Voltmeter or Digital Multimeter

2.    Ammeter

3.    Bread Board

4.     Diodes ( Si- 1N4007)

5.    Resistors 1k

6.    0 - 30 V dc power supply

Forward Bias Circuit Diagram

Theory:-

In electronics, a diode is a two-terminal electronic component that conducts electric current in only one direction. The term usually refers to a semiconductor diode, the most common type today, which is a crystal of semiconductor connected to two electrical terminals. Today most diodes are made of silicon, but other semiconductors such as germanium are sometimes used.

The Shockley ideal diode equation or the diode law:-

                                       

Where

I is the diode current,

I_S is the reverse bias saturation current,

V_D is the voltage across the diode,

V_T is the thermal voltage, and

n is the emission coefficient, also known as the ideality factor. The emission coefficient n varies from about 1 to 2 depending on the fabrication process and in many cases is assumed to be approximately equal to 1.

where k is the Boltzmann constant, T is the absolute temperature of the p-n junction, and q is the magnitude of charge on an electron.V_T is approximately 25.85 mV at 300 K .

DC forward resistance: It is the opposition by diode to the DC. It is measured by the ratio of DC voltages across the diode to the resulting DC current through it. 

Procedure:-

1. Connect the circuit as shown in the figure.
2. Increase the supply voltage in steps of 0.1v upto 1v then in steps 0.5v upto 5volts. Then measure current I_D , voltage drop across the diode V_d and  record the results in Table.
3. Plot on a graph paper I_D versus V_D for the silicon  diode. Complete the curves by extending the lower region of each curve to the intersection of the axis at I_D = 0 mA and V_D = 0 V.

Result  Table (Ge, Si)

Vsource	Vd	Id
.5V
1V
1.5V
2V
2.5V
3V
3.5
4V
4.5V
5V

Expected I-V characteristics:-

V-I Characteristics of Zener Diode

 Objective:-

1.      Design the circuit diagram

2.      Take the reading and draw the characteristics curve

3.      Determine the DC forward and Reverse  resistance.

4.      Determine the  Zener Voltage (Vz)

Equipments required:-

1.    Voltmeter or Digital multimeter

2.    Ammeter

3.    Bread Board

4.    Zener Diode

5.    Resistors 1k

6.    0 - 30 V dc power supply

Theory:-

A Zener diode is a type of diode that permits current not only in the forward direction like a normal diode, but also in the reverse direction. If the voltage is larger than the breakdown voltage known as "Zener knee voltage" or "Zener voltage". The forward characteristic of the zener diode is same as that of a pn junction diode i.e. as the applied potential increases the current increases exponentially. Applying a negative potential to the anode and positive potential to the cathode reverse biases the zener diode. As the reverse bias increases, the current increases rapidly in a direction opposite to that of the positive voltage region. Thus under reverse bias condition breakdown occurs.

  

Forward  Bias Circuit Diagram

Reverse  Bias Circuit Diagram

Procedure:-

Forward-Bias:-

1. Construct the circuit as shown in figure for forward biased zener diode.

2.Take the reading from the voltmeter and the ammeter  and fill the table 

    by increasing the input DC voltage.

3. Plot I_d vs V_d in a graph to get the forward biased characteristics.

Reverse Bias:-

1. Construct the circuit as shown in figure for reverse biased zener diode.
2. Take the reading from the voltmeter and the ammeter  and fill the table by increasing the input DC voltage.
3. Plot I_d vs V_d in a graph to get the reverse biased characteristics.
4. Find the voltage at the point where Id decreases sharply to get the zener voltage.

Result Table ( Forward Bias)

V source	Vd	Id
.5V
1V
1.5V
2V
2.5V
3V
3.5
4V
4.5V
5V

Reverse Bias

V source	Vd	Id
1V
2V
3V
4V
5V
6V
7V
8V
9V
10V

Expected I-V characteristics (Forward Bias):-

Expected I-V Characteristics (Reverse bias):-