Experiment 2 : Diode V-I characteristics

Name : Arun Kumar Singh

Roll No. : 10002034

Group No. : 3

Group member : Adit Bhardwaj(10002004)

Date : 11/8/2011

EXPERIMENT -2 AIM: A.To obtain the V-I characteristics of a diode.

B. To obtain the V-I characteristics of a LED.

C. To observe the voltage across a LED and a resistor connected in series when a saw tooth voltage signal is applied.

EQUIPMENTS USED: Ge- diode, transistor, 5v DC source, multimeter,port,68k resistor,LED,1k resistor,bread board,function generator and digital storage oscilloscope(DSO).

PROCEDURE:

(1) V-I characteristics of a diode

1. At the starting connect the elements as shown in the following circuit diagram:-

2. We now make the voltage zero in voltmeter by rotating the nob of the port.

3. Next rotate the nob so as to increase the voltage in voltmeter by .020 volt and note the corresponding current.

4.Plot the graph between V & I to obtain V-I characteristics of the diode.

(2) V-I characteristics of a LED

1. Connect the components as shown in the circuit diagram.

2. Next vary the voltage through variable voltage source .

3. Note the voltage across LED and resistor.

4.Current through the circuit and LED =i=Vr/r

where Vr = voltage across resistor and r= resistance of resistor.

5. Plot V-I characteristic of LED.

(3) Wave form across LED and resistor

1. Connect the elements as shown in the circuit diagram.

2. Supply a sawtooth wave of peak voltage 2v and frequency 100Hz.

3. Now observe the voltage wave form across LED and resistor by using DSO.

OBSERVATION :

(1) V-I characteristics of a diode

It was observed that as we increase the voltage the current was almost zero till voltage reached 60mV .

On further increasing the voltage current increased slowly till voltage reached 0.4 V.

After then the current increased abruptly even with a small change in voltage.

Explanation : Initially the current is 0 as the voltage across it is less than its cut-in voltage . As we increase the voltage the current slowly start increasing. And after a point the current increase abruptly when the external voltage is greater than the cut-in voltage and for a small increase in voltage the current increases abruptly.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90

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Series2

(2) V-I characteristics of a LED

V-I characteristics of GE-diode

Scale:-

on x-axis voltage 1 unit = .5 volt

on y-axis current 1 unit =1mA

It was observed that as we increase the voltage the intensity of the light was almost zero. On further increasing the voltage light increased slowly till voltage reached. After then the light increased even with a small change in voltage.

Explanation : Initially the current is 0 as the voltage across LED is less than its cut-in voltage . As we increase the voltage the light intensity slowly start increasing. And after a point the light increase fully when the external voltage is greater than the cut-in voltage and for a small increase in voltage the current and hence increases abruptly.

(3) Wave form across LED and resistor

When an saw-tooth wave is passed through the circuit a part of the voltage is used to over the cut-in voltage and hence a part of signal wave appears across the diode(LED) and the remaining part appears at resistor.

Explanation : This is because when the signal voltage excide the cut-in voltage the current start flowing through the diode freely and hence no more voltage is

dropped across the diode. Now if voltage is increase even more it only appears across the resistor.

RESULT :

(1) The cut-in voltage of the diode from the graph is .4V.

(2) The cut-in voltage of the LED is

(3) The wave form observed across the LED and resistor are as follows.