Assalam o Alaikum ! Today I want to Share my Assignment of Power Electronics , Hope You find it Informative.
Diode
Diode is a simple Semiconductor device
which is used for many purposes in electronic applications.
Diode is specially known for conversion
of AC to DC or Rectification process. It is opted for its unique
characteristics such as Uni-Directional current provision and
infinite resistance to the Reverse current.
SYMBOL:
Diode consists of two doped
semiconductors, one of a P-type and other of N-type. When Tetravalent
semiconductor is doped with pentavalent impurities , then electrons
are the majority carriers and N-type semiconductor is formed.
Secondly, P-type with holes as the majority carriers is formed, when
trivalent impurities are added to the tetravalent semiconductor
material. After that, P-type semiconductor and N-type Semiconductor
are diffused together. By Diffusion, electrons from N-type region
flow to P-type region and holes flow from P-type to the N-type region
leaving behind negatively charged ions. In this process, electric
field is created with opposite polarities to the respective (n-type
or p-type) regions which blocks the further transfer of both carriers
and as a result, a potential barrier is formed in between the
semiconductors which is called Depletion region.
This PN juction can be used according
to the need and in a controlled manner. It can be used in three
modes, Zero bias , Forward Bias and Reverse Bias. In Zero Bias mode,
it remains at its neutral behaviour. In Forward Bias mode, a
potential difference is applied to the junction where P-type material
is connected with the positive terminal and N-type is connected with
the negative terminal of the Source.
When this arrangement is made ,
opposite polarity potential (w.r.t depletion region) breaks the
potential barrier(inside) and flow of charges is started from both
ends and as a result the current is observed.
In Reverse Bias, P-type is connected
with negative terminal and N-type is connected with the positive
terminal of the source.
This arrangement keeps the majority
carriers of both materials away from breaking the depletion region
and source potential(outside) attracts the majority carriers which
results in increment of depletion region and a large voltage is
observed.
Diodes are used in almost every
electronic device both on small and large scales . However, diode
needs some modification in high power applications. Diode undergoes
some problems such as ability to conduct high current in forward bias
and to hold high voltage and avoid breakdown in reverse bias. To
overcome these problems, concept of Power diodes is
introduced.
Power Diode
Power Diode
Power diode is built with vertical
orientation to provide extra cross-sectional area which is required
to handle large amount of current . The other problem of controlling
breakdown voltage in reverse bias is overcome by controlling the
relative factors.
Breakdown occurs due to the high
electric field in potential barrier. Electric field and depletion
width has inverse relation (E=V/d), so to control the break down at
very high voltage, depletion width has to be altered, and to alter
the depletion width, Doping of the material has to be changed. This
is done by the following arrangement of normal and less doped
semiconductors.
In this arrangement,an extra layer of
N-type material is introduced. Here, N-type in the middle region is
less doped and the other P-type and N-type materials are normally
doped. When the diode comes in reverse bias mode, it sees a large
potential barrier across the lightly doped N-type region, which makes
it able to withstand more voltage than normal. Extra layer used here,
has to provide required majority carriers to maintain the current
without reduction during the forward bias mode.
Major Differences
Major Differences
1- Design
Simple diodes consist of a simple PN
junction. They are smaller in size and lighter in weight, while power
diodes are in modified form and they are larger and heavier normally.
Power diodes are usually available in metal form.
2- Voltage Rating
Simple diodes are used in normal low
power components so they have a relatively low voltage ratings as
compared to power diodes. Power diodes can have very high voltage
ratings usually in thousands of volts.
3- Current Rating
Power diodes have a high hand in
Current ratings over normal diodes , that can be in several hundred
amperes.
4-Temperature
Major probelm in handling high power
applications is the generation of heat and temperature. Power diodes
have the accessiblity of operation at higher temperature whereas
normal diodes do not need this feature in high priority.
5- Cost
Power Diodes are costly as compared to
the simple diodes due to the additional components and features.
Copyright : M.Shahzaib S. Qureshi
----------------------------------------------------
The End -----------------------------------------------
.jpg)