LED and Varactor diode

1. LED and Varactor
diode
By – Anvesha Kaushik

2. Light
Emitting
Diode (LED)
LED is a semiconductor device, which can emit
light when an electric current passes through it.
When current passes through LED, the holes
from p-type semiconductors recombine with
electrons from n-type semiconductors. It allows
the current to flow in the forward direction and
blocks current in reverse direction.

3. LED Symbol and Circuit

4. Working of LED
When the diode is forward biased, the minority electrons are sent from p to n
while the minority holes are sent from n to p. At the junction boundary, the
concentration of minority carriers increases. The excess minority carriers at the
junction recombine with the majority charges carriers and dissipate energy.
The energy is released in the form of photons on recombination. If the
semiconductor material is translucent, the light is emitted and the junction
becomes a light source, i.e. a light emitting diode(LED).

5. Advantages of LED
• LEDs are fast operating devices and can be turned on/off in order of use.
• LEDs consume less power, and they require low operational voltage.
• No warm-up time is needed for LEDs.
• The emitted light is monochromatic.
• They exhibit long life and ruggedness.

6. Applications
of LED
Used for TV back-lighting
Used in displays
Used in Automotives
LEDs used in the dimming of lights
Can be used to design visual display.

7. Varactor Diode
Voltage variable capacitor diodes (VVCs) are also known as varicaps,
varactors and turning diodes. Basically, a VVC is a reverse biased
diode and its capacitance is the junction capacitance.
Itis a type of diode whose internal capacitance varies with respect to
the reverse voltage. It always works in reverse bias condition and is a
voltage-dependent semiconductor device.

8. Symbol of Varactor Diode

9. Working of Varactor Diode
Since the width of depletion region at a p-n junction depends upon
the reverse bias voltage, a large reverse bias produces a wide
depletion region. The depletion region acts as a dielectric between
two conducting plates, thus junction behaves as a capacitor. The
depletion region capacitance is proportional to the area and
inversely proportional to the width of depletion layer.

10. Applications
of Varactor
Diode
• They can be used as frequency modulators
and RF phase shifters.
• They can be used as frequency multipliers in
microwave receivers.
• They are used to change the capacitance in
tank LC circuits.

11. Thank You!!