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P-N Junction

When a p-n junction is

formed, some of the free

electrons in the n-region

diffuse across the

junction and combine withholes to form negative

ions. In result they leave

behind positive ions at

the donor sites as shownin the figure below.

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P-N Junction (Depletion Region)

When a p-n junction

is formed, some of

the electrons from the

n-region which havereached the

conduction bandare

free to diffuse across

the junction andcombine with holes.

http://hyperphysics.phy-astr.gsu.edu/hbase/solids/dsem.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/solids/dsem.html

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P-N Junction (Depletion Region)

Filling a hole makes a negative ion and

leaves behind a positive ion on the n-side.

A space charge builds up, creating a

depletion region which inhibits any further

electron transfer unless it is helped by

putting a forward bias on the junction

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P-N Junction (Depletion Region)

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DIODE

A P-N junction device

having two terminals

anode and cathode is

called diode.

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Diode Characteristics

Forward Biased

If the voltage is applied in such a way that

positive terminal of the battery is connected to

the P-type terminal (Anode) and negative withthe N-type terminal (cathode) of a diode. This

assists electrons in overcoming the space

charge in depletion region. Electrons will flow

with very small resistance in the forwarddirection.

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Forward Biased

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Forward Biased

Silicon diodes require 0.7V to assist electrons in

overcoming the space charge in depletion region

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Forward Biased

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Reverse Biased:

If the voltage is applied in such a way that

positive terminal of the battery is

connected to the N-type of the diode and

negative with the P-type of a diode then itfurther impedes the flow of electrons

across the junction.

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Reverse Biased:

Reverse Bias causesto widen the depletionregion

During reverse biaseda very small amountof current flows whichis in pico amperes.This current is calledthe reverse saturationcurrent or leakagecurrent.

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Diode Characteristic Curve

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Diode as a Rectifier

The process of converting AC in to DC is

called Rectification. The most common

and widely used application of diode is

rectification.

Half Wave Rectifier

Full Wave Rectifier

Bridge Rectifier

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Half Wave Rectifier

The simplest kind of rectifier circuit is the

half-wave rectifier.

It only allows one half of an AC waveform

to pass through to the load.

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Half Wave Rectifier

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Full Wave Rectifier

To rectify AC power to obtain the full use

ofboth half-cycles of the sine wave, a

circuit consisting of two diodes is used and

is called full wave rectifier.

We use the centre tapped transformer in it

which increases the cost as well as size of

the circuit

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Full Wave Rectifier