Difference Between Normal and Power Diode

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 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

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 -----------------------------------------------