EXPERIMENT-5
LED AND SOLAR CELL CHARACTERISTICS
AIM: To study V-I Characteristics of Light Emitting Diode (LED) and Solar cell
LED Characteristics
.
APPARATUS: Light emitting Diode Characteristics board comprising of:
1. Light emitting diode
2. 0-5V variable Supply for Light emitting diode
3. 20mW Digital Optical power meter to measure optical power of Light emitting diode
4. 20V Digital Voltmeter to measure voltage across Light emitting diode
5. 200mA DC Digital Ammeter to measure Light emitting diode Current
THEORY: - A p-n junction diode, which emits light on forward biasing, is known as light
emitting diode. The emitted light may be in the visible range or invisible range and the intensity
of light depends on the applied potential.
PRINCIPLE: - In a p-n junction charge carrier recombination takes place when the electrons
cross from the n-layer to the P-layer. The electrons are in the conduction band on the p-side
while holes are in the valence band on the p-side. The conduction band has a higher energy
level compared to the valence band and so when the electrons recombine with a hole the
difference in energy is given out in the form of heat or light. In case of silicon or germanium,
the energy dissipation is in the form of heat, whereas in case of gallium-arsenide and gallium
phosphide, it is in the form of light. But this light is in the invisible region & so these material
cannot be used in the manufacture of LED. Hence gallium – arsenide phosphide which emits
light in the visible region is used to manufacture an LED.
CIRCUIT DIAGRAM:
CONSTRUCTION: An n-type layer is grown on a substance and a p-type layer is grown over
it by diffusion process. The P-layer is kept at the top because carrier recombination takes place
in it. The terminals anode and cathode are taken out of the n-layer and P-layer respectively.
The anode connections are made at the edge in order to provide more surface area for the
emission of light. A metal film is applied to the bottom of substance to reflect light to the
surface of the device and also to provide connection for the cathode terminal. Finally the
structure are provided with an encapsulated (cover) to protect them from destruction
ADVANTAGE: -
1. Works on low voltage and current and hence consumes less power.
2. Require no warm up time.
3. Can be switched ON and OFF at a faster rate.
4. Long lifetime.
5. Small size and less weight.
Procedure for V/I characteristics of a Light emitting diode:
1. Connect the Light emitting diode circuit as per the circuit diagram.
2. Slowly increase supply voltage using variable Power supply using coarse and fine knobs.
3. Note down current through the Light emitting diode at increasing values of Light
emitting diode voltage of 0.5V, 1.0V, 1.5V, 2.5 V.
4. Do not exceed current limit of 30mA else the Light emitting diode may get damaged.
5. Plot a graph of Light emitting diode voltage V/s Light emitting diode current .
OBSERVATION TABLE:
For V/I characteristics of LED
S. No. LED Voltage LED Current
V (volt) I (mA)
1
2
3
4
5
6
7
8
9
10
MODEL GRAPH:
V/I characteristics of LED
Solar Cell Characteristics
APPARATUS:
1. Solar Cell/Photovoltaic cell mounted on the wooden base.
2. Single directional mercury coated variable intensity source.
3. Voltmeter.
4. Ammeter.
5. Load resistance.
THEORY:
Sunlight consists of little particles of solar energy called photons. As the photovoltaic cell is
exposed to this sunlight, many of the photons are reflected, pass right through or absorbed by
the solar cell.
When enough photons are absorbed by the negative layer of the photovoltaic cell, electrons
are freed from the negative semiconductor material. Due to the manufacturing process of the
positive layer, these freed electrons naturally migrate to the positive layer creating a voltage
differential, similar to a household battery.
When the 2 layers are connected to an external load, the electrons flow through the circuit
creating electricity. Each individual solar energy cell produces only 1-2 watts. To increase
power output, cells are combined in a weather-tight package called a solar module. These
modules (from one to several thousand) are then wired up in serial and/or parallel with one
another, into what’s called a solar array, to create the desired voltage and amperage output
required.
Due to the natural abundance of silicon, the semi-conductor material that PV cells are
primarily made of, and the practically unlimited resource in the sun, solar power cells are
very environmentally friendly. They burn no fuel and have absolutely no moving parts which
makes them virtually maintenance free, clean, and silent.
The Fill Factor determines the maximum extracting power of a solar cell. The Fill factor is
defined as the ratio of the maximum power from the solar cell to the product of Voc and Isc.
The short circuit current Isc, is the maximum current from the solar cell and occurs when the
voltage across the solar cell is approximately zero. Voc is the open circuit voltage.
PROCEDURE:
1. Connect the circuit as per the circuit diagram .
2. Place the solar cell at a particular distance say 1cm from the variable light source.
3. Vary intensity of the light source, note down the voltage and current in the tabular
column.
4. Next note the short circuit current Isc, when the voltage across the solar cell is zero &
open circuit voltage Vo by removing the load resistance across the solar cell.
5. Calculate power P=VI for each reading.
6. Plot the graph between the voltage Vs Current , mark the maximum power point,
7. Repeat the experiment by changing the distance between the solar cell & light source.
CIRCUIT DIAGRAM:
MODEL GRAPH:
Maximum Power
Isc
point (MPP)
Imax
CURRENT mA
Open circuit
voltage Vo
Vmax
0
VOLTAGE IN mV
OBSERVATIONS:
S.NO DISTANCE BETWEEN VOLTAGE IN CURRENT IN P=VI
THE LIGHT SOURCE & mV mA
SOLAR CELL IN CMS
1. SHORT CIRCUIT CURRENT Isc is
2. OPEN CIRCUIT VOLTAGE Voc is
3. MAXIMUM PEAK POINT(MPP) is
4. Fill Factor(FF) =MPP/ (Voc* Isc) =
RESULT:
V-I characteristics of LED and Solar cell has been studied.
The Fill Factor of Solar Cell is found to be__________.
