Objectives:
study the theory of PN junction diode.
study the Working principal and operation mechanism of PN junction diode.
plot the VI characteristic of PN junction diode (Silicon).
cut-in voltage for Silicon and P-N Junction diodes.
static and dynamic resistances in both forward and reverse biased conditions.
Equipment's and Tool:
Oscilloscope
Variable power supply
Digital multimeter
Circuit board
Diode (Silicon)
Variable resisters
Connecting wires
Theory:
Diode:
Diode, an electrical component that allows the flow of current in only one direction.
OR
Diodes are two-terminal electronic devices, made out of semiconductor materials.
In circuit diagrams, a diode is represented by a triangle with a line across one vertex.
The most common type of diode uses a p-n junction. In this type of diode, one material
(n) in which electrons are charge carriers abuts a second material (p) in
which holes (places depleted of electrons that act as positively charged particles) act as
charge carriers.
When a voltage is applied across the junction, a current flow in response, but the i-v
relationship is extremely nonlinear. The non-linearity will force us to modify our
approach to analyzing circuits
At their interface, a depletion region is formed across which electrons diffuse to fill holes
in the p-side. This stops the further flow of electrons.
Although in the real world, diodes cannot achieve zero or infinite resistance. Instead, a
diode will have negligible resistance in one direction (to allow current flow), and very
high resistance in the reverse direction (to prevent current flow). A diode is effectively
like a valve for an electrical circuit.
, Fig no 5.1 Diode:
Forward biased:
The process by which, a p-n junction diode allows the electric current in the presence
of applied voltage is called forward biased p-n junction diode.
In forward biased p-n junction diode, the positive terminal of the battery is connected to
the p-type semiconductor material and the negative terminal of the battery is connected
to the n-type semiconductor material.
Fig no 5.2 Forward biased
Reversed biased:
Reverse bias usually refers to how a diode is used in a circuit. If a diode is reverse biased,
the voltage at the cathode is higher than that at the anode. Therefore, no current will
flow until the electric field is so high that the diode breaks down.
, the p-type material is now connected to the negative side of the applied voltage, the
holes in the p-type material are pulled away from the junction, causing the thickness of
the depletion layer to increase.
because the n-type region is connected to the positive side, the electrons will also be
pulled away from the junction.
Therefore, the depletion layer widens, and does so increasingly with increasing reverse-
bias voltage.
This increases the voltage barrier causing a high resistance to the flow of charge carriers
thus allowing only a very small electric current to leak across the PN junction.
Fig no 5.3 Reversed Biased
Application of diode:
Diode as a Rectifier:
The most common and important application of a diode is the rectification of AC power to
DC power. Using diodes, we can construct different types of rectifier circuits. The basic types
of these rectifier circuits are half wave, full wave center tapped and full bridge rectifiers.
study the theory of PN junction diode.
study the Working principal and operation mechanism of PN junction diode.
plot the VI characteristic of PN junction diode (Silicon).
cut-in voltage for Silicon and P-N Junction diodes.
static and dynamic resistances in both forward and reverse biased conditions.
Equipment's and Tool:
Oscilloscope
Variable power supply
Digital multimeter
Circuit board
Diode (Silicon)
Variable resisters
Connecting wires
Theory:
Diode:
Diode, an electrical component that allows the flow of current in only one direction.
OR
Diodes are two-terminal electronic devices, made out of semiconductor materials.
In circuit diagrams, a diode is represented by a triangle with a line across one vertex.
The most common type of diode uses a p-n junction. In this type of diode, one material
(n) in which electrons are charge carriers abuts a second material (p) in
which holes (places depleted of electrons that act as positively charged particles) act as
charge carriers.
When a voltage is applied across the junction, a current flow in response, but the i-v
relationship is extremely nonlinear. The non-linearity will force us to modify our
approach to analyzing circuits
At their interface, a depletion region is formed across which electrons diffuse to fill holes
in the p-side. This stops the further flow of electrons.
Although in the real world, diodes cannot achieve zero or infinite resistance. Instead, a
diode will have negligible resistance in one direction (to allow current flow), and very
high resistance in the reverse direction (to prevent current flow). A diode is effectively
like a valve for an electrical circuit.
, Fig no 5.1 Diode:
Forward biased:
The process by which, a p-n junction diode allows the electric current in the presence
of applied voltage is called forward biased p-n junction diode.
In forward biased p-n junction diode, the positive terminal of the battery is connected to
the p-type semiconductor material and the negative terminal of the battery is connected
to the n-type semiconductor material.
Fig no 5.2 Forward biased
Reversed biased:
Reverse bias usually refers to how a diode is used in a circuit. If a diode is reverse biased,
the voltage at the cathode is higher than that at the anode. Therefore, no current will
flow until the electric field is so high that the diode breaks down.
, the p-type material is now connected to the negative side of the applied voltage, the
holes in the p-type material are pulled away from the junction, causing the thickness of
the depletion layer to increase.
because the n-type region is connected to the positive side, the electrons will also be
pulled away from the junction.
Therefore, the depletion layer widens, and does so increasingly with increasing reverse-
bias voltage.
This increases the voltage barrier causing a high resistance to the flow of charge carriers
thus allowing only a very small electric current to leak across the PN junction.
Fig no 5.3 Reversed Biased
Application of diode:
Diode as a Rectifier:
The most common and important application of a diode is the rectification of AC power to
DC power. Using diodes, we can construct different types of rectifier circuits. The basic types
of these rectifier circuits are half wave, full wave center tapped and full bridge rectifiers.
