This ppt will explain the basic operation, advantages, disadvantages, applications of LED and operation, characteristics and applications of varactor diodes.

1. SEMINAR ON BASIC
ELECTRONICS
TOPIC-LED & VARACTOR DIODES
AVNEET SINGH LAL
EC-3

2. LED

3. ABOUT LED
 LED is an opto-electronic device which emits a narrow
bandwidth of visible or invisible light when its internal diode
junction is stimulated by a forward electric current or
voltage.
 LEDs convert electrical energy into light energy.
 The material used for LEDs are the direct Band Gap
Semiconductors which are made from group 3rd and group 5th
elements. For eg.- GaAs

4. OPERATION OF LED
 The operation of LED is based on the phenomenon
of electro luminance.
 The recombination of charge carriers takes place in
a forward p-n junction as the electrons cross from
the n-region and recombine with holes existing in
p-region.

5. ADVANTAGES OF LED
 LEDs are small in size and can be used to form
numeric and alpha numeric display in high density
matrix.
 LEDs are rugged.
 They need moderate power.
 High Lighting Efficiency
 Long Life
 High Reliability & Safety
 Environment Friendly
 Excellent Colour Rendering
 No warm up period

6. DISADVANTAGES
 A very limited variety and selection for your home
compared to other types of lighting.
 Hard to find in smaller towns where consumers may
have a smaller interest in this lighting alternative.
 Significantly more expensive than regular lighting
and not budget conscious.
 Although they are available in many colours, the
quality of the colours is not quite as good as with
regular lighting.

7. APPLICATIONS
 Medical Instrumentation
 Bar Code Readers
 Fibre Optic Communication
 Digital Cameras
 Laptops
 Traffic Signals
 Rail
 Tower Lights

8. VARACTOR DIODE

9. ABOUT VARACTOR DIODES
 A microwave solid-state device.
 Also known as a parametric diode, tuning diode or
varicap diodes
 A nonlinear device
 Provides a voltage-dependent variable capacitance
SYMBOL

10. OPERATION
 It has a p-n junction of semiconducting
material and is always reverse biased.
 The depletion zone width depends on the
applied voltage and this makes the
capacitance vary with the applied
voltage.

11. CHARACTERISTICS
 Low noise
 Low cost
 High reliability
 Light weight
 Small size
 Increase in reverse bias
of varactor diode increases
the capacitance as shown
in the figure.

12. APPLICATIONS
 Variable reactor in microwave circuits.
 It can be used for voltage tuning of
LC resonant circuit.
 It is used for generation of FM
Waves.

13. CONCLUSIONS
 Varactor diodes in reverse bias operates as
variable capacitor as reverse voltage varies, where:
 Depletion region : Dielectric (Insulator)
 P - N Regions : Plates of capacitor
 Width of Depletion region : Distance of separation

14. THE END
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