lecture about diode

1. Diodes

2. Diodes
Type of Diodes

3.  When phosphorus is added to Silicon, every phosphorus atom’s four
electrons are locked up with electrons of four neighboring Silicon
atoms.
 The 5th electron of phosphorus atom remains free to float
 Free electrons are moved under the influence of the applied electric
field. Since electrons have negative charge they are attracted towards
the positive terminal.
N-Type Silicon
Diodes

4. P-Type Silicon
 When boron is added to Silicon, every boron atom’s three electrons are
locked up with electrons of three neighboring Silicon atoms.
 However, a hole is created within one boron atom and a neighboring
Silicon atom.
 Holes may be thought of positive charged particles and as such they
move through an electric field in a direction opposite to that of
electrons.
Diodes

5. Circuit Symbols:
 Diode made from a combination of 2 semiconductors, P-
type (Anode) and N-type (Cathode) material.
 The joint between the P-type and N-type material is
called PN junction.
 Current flow: Diode allows current to pass in only one
direction from the positive (anode) terminal to the
negative (cathode) terminal .
Diodes

6. Diode: How it Works
Diodes
When a diode is connected to a battery as shown, electrons
from the n-side and holes from the p-side are forced toward
the center by the electrical field supplied by the battery. The
electrons and holes combine causing the current to pass
through the diode. When a diode is arranged in this way, it is
said to be forward biased.

7. Diode: How it Works
Diodes
When a diode is connected to a battery as shown, electrons
from the n-side and holes from the p-side are forced toward
the center by the electrical field supplied by the battery. The
electrons and holes combine causing the current to pass
through the diode. When a diode is arranged in this way, it is
said to be forward biased.

8. Diode I / V Characteristic
Diodes
 The axes (top right) show the forward conduction of the diode when the
anode is positive and cathode negative. Initially no current flows until the
applied voltage is at about the forward junction potential, after which a
small increase in voltage giving a large increase in current.
 The axes (bottom left). Here, although the voltage increases, hardly any
current flows. If a high enough reverse voltage is applied however,
there is a very high current suddenly flows. Diode will be destroyed

9. Rectification − changing A.C. power to D.C. power.
DIODES APPLICATION
I. Half way rectifier:
(Rectifying power supply circuit)
 A half-wave rectifier is a circuit that converts an AC current
into a DC signal
 During the conversion process, positive polarity of AC passed
to output, while negative polarity are blocked
 The name half-wave is derived from the fact that half the AC
are passed to the output

10. II. Full way Two diodes rectifier:
Rectification − changing A.C. power to D.C. power.
(Rectifying power supply circuit)
DIODES APPLICATION
 The full-wave rectifier is the equivalent of two half-wave rectifiers
 In other words, Diode #1 will allow current to flow during
the positive half of the AC sine wave and Diode #2 will allow
current to flow during the negative half of the AC sine wave.
Both provide a positive Vout to the load.
This symbol represents a transformer – a device for
changing the high voltage mains AC into low voltage AC

11.  The full-wave bridge rectifier is
designed to convert an AC sin-
wave to a full-wave DC signal
III. Full way bridge rectifier:
Rectification − changing A.C. power to D.C. power.
(Rectifying power supply circuit)
DIODES APPLICATION
First Half Cycle Second Half Cycle

12. Demodulation − (TV and Radio sets) : recovering audio
information from TV / radio signals.
DIODES APPLICATION

13. Lighting − light emitting diodes (LED) , replace filament
lamps and Indicator light in electronic circuit.
These diodes are made from a range of
semiconductor materials, depending on the
color of light required:
Gallium Arsenide Phosphide (GaAsP) = Red
Gallium Phosphide (GaP) = Green
Gallium Indium Phosphide (GaInP) = Yellow
DIODES APPLICATION

14. Lighting − (RGB LED).
DIODES APPLICATION

15. Stabilization. − Zener diodes can be used to set very
precise voltage values in such circuits as DC power supply.
 In use they are reverse biased. No current will flow (apart from a very
small leakage current) until the "breakdown voltage" is reached.
 The Zener diode is like a general-purpose signal diode. When biased
in the forward direction it behaves just like a normal signal diode,
DIODES APPLICATION

16.  Voltage regulator − Zener diodes can be used to set very
precise voltage values in such circuits as DC power supply.
 As the input voltage increases the current
through the Zener diode increases but the
voltage drop remains constant - a feature of
Zener diodes. Therefore since the current in the
circuit has increased the voltage drop across the
resistor increases by an amount equal to the
difference between the input voltage and the
zener voltage of the diode.
 As long as the input voltage is a few volts more
than the desired output voltage, the voltage
across the Zener diode will be stable.
DIODES APPLICATION

17. Protection − diodes can be used to protect circuits from
being damaged by such things as wrong polarity supply
connection, and abnormally high voltages or currents.
A project can be protected from reverse voltage by placing a diode on
the positive input line.
For reverse-voltage protection, a diode can be placed across the
input.
DIODES APPLICATION

18.  Infrared LEDs
 Used in things like TV remotes to send small pieces of
information in the form of invisible light
 Emit light outside of the normal visible spectrum
 Ultraviolet LEDs.
 They’re also used for disinfecting surfaces,
because many bacteria are sensitive to UV
radiation.
DIODES APPLICATION

19.  Laser Diodes.
 Laser diodes find wide use in telecommunication
as easily modulated and easily coupled light
sources for fiber optics communications.
 They are used in various measuring instruments, such as
rangefinders
 Another common use is in barcode readers
 Visible lasers, typically red but later also green, are common as
laser pointers.
 used in the printing industry both as light sources for scanning
(input) of images and for very high-speed and high-resolution
printing
 red laser diodes are common in CD players, CD ROMs and DVD.
DIODES APPLICATION
 signal sensor in radar