Applied Instrumentation Lab 8EI7

Experiment No. – 4

Object: - Plot V-I and P-I Characteristics of (LED) Light Emitting Diode.

Apparatus: LED Trainer module with bread board, 1KΩ Resistor, Voltmeter, Ammeter

Theory: - A Light Emitting Diode (LED) is a semiconductor diode mode by creation of junction of n type and p type material. Thus the principle of LED action works precisely the same way that we described the creation of permanent light radiation. Alternatively w can say that the external energy provided by V excites electrons at the conduction band to the valence band and recombine with hole. The net result is the light radiation. It consists of an encapsulated chip of semiconductor diode with a suitable lens. The length of anode terminal is greater than cathode terminal. LEDs are based on the semiconductor diode. When the diode is forward biased (switched on), electrons are able to recombine with holes and energy is released in the form of light. This effect is called electroluminescence and the color of the light is determined by the energy gap of the semiconductor. The LED is usually small in area (less than 1 mm2) with integrated optical components to shape its radiation pattern and assist in reflection.

Fig. 1.1 Working Principle of LED

Procedure: - Forward Bias

1. Construct the equipment as shown in the figure 2. Set the bias selection switch in forward bias position 3. Set the fiber cable between LED and PD 4. Now set bias control Pot in particular level(-0.6) 5. Step by step vary the LED intensity bias control POT.6. Increases the voltage applied to diode gradually in steps and note the ammeter and

voltmeter readings.

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Applied Instrumentation Lab 8EI7

7. Now find the current flowing through photodiode by using below formula I = Voltage across points P1 and P2 / 1 KΩ

8. Plot the graph between voltage across power and current

Reverse Bias

1. Construct the equipment as shown in the figure 2. Set the bias selection switch in reverse bias position 3. Vary the POT2 to max level ie., high intensity in LED 4. Set the fiber cable between LED and PD 5. Now step by step increase the bias control voltage in 1.28V to 5V 6. Note down voltage across photo diode VPD and voltage across resistor VR 7. Now find the current flowing through photodiode by using below formula

I = Voltage across points P1 and P2 / 1 KΩ

8. Plot the graph between voltage across photodiode VPD and current.

Fig. 1.2 Circuit Diagram

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Applied Instrumentation Lab 8EI7

Fig. 1.3 V-I Characteristics of LED

Observation: -

S. N. Voltage across resistor

Voltage across LED

Current through resistor

Current through LED

1.

2.

3.

4.

5.

Result: - Thus we have plotted the V-I and P-I Characteristics of LED.

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