POWER SUPPLY DESIGN USING ZENER DIODE

Introduction:

The Zener diode is a two-terminal active electronic component, whose V-I characteristics are just like PN-diode. The working of Zener diode as follows, when the diode is forward biased it acts as ON switch. When it is reverse biased the Zener diode acts as a voltage regulator that is when the input voltage is more than the Zener breakdown voltage (Vz)  the output voltage (Vo) is equal to the Zener breakdown voltage.

Working:

          If we recall the basics of semiconductors a PN-diode is formed by the combination of P-type semiconductor and N-type semiconductor, because of the excessive electrons (donors) in N-type material and protons (acceptors) in P-type material a junction is formed due to the combination of  both materials which is termed as a potential barrier or forward voltage barrier (Vf).

A diode can be biased in three ways which are described as.

Unbiased semiconductor diode:

            This is a condition where the no voltage is applied to the diode, in this condition the diode is an ideal state that is it does nothing simply an open switch. By the principle of diffusion, the holes in P-type material and electrons in N-type materials tend to go towards lower concentration. This results in forming the depletion region which is also known as a potential barrier (Vf).

            In this process, the holes from the P-type material accumulate at the N-type material in the same way the electron in N-type accumulate at P-type material this results in a voltage threshold. The voltage threshold changes depending on the material used. 0.2V for Germanium and 0.6V for Silicon type.

Vth ->Vf -> 0.3V for Germanium, 0.7 for Silicon.

P-type terminal is termed as Anode (A)

N-type terminal is termed as cathode (K)

diode in unbiased state

                                                                           Fig 1: diode in unbiased state.

Forward biased semiconductor diode:

            In this condition the anode (A) is connected to the positive rail, the cathode (K) is connected to the negative rail of the power supply (Vin). Let’s assume the power supply is a variable type. The following expression gives the overview and the behaviour of the diode.

  • Vin<Vf -> diode is in OFF state therefore no conduction
  • Vin=Vf -> diode starts conduction with minimal current than previous condition.
  • Vin>Vf ->diode goes into saturation mode comes to ON state results to more flow of current from Anode to cathode.

From the above the first and second conditions are used to make the diode as ON,OFF switch.

Note: In this mofe the behaviour of the zener diode is similar to the PN diode.

Reverse biased Semiconductor diode:

            This mode is quite opposite to the forward biased that is Anode (A) is connected to the –Ve rail of the power supply and cathode (K) is connected to the +Ve rail of the power supply. In this mode, the depletion region moves away from its origin this will continues until the depletion regions attain its maximum. After this, if the Vin starts to increase this will result in a large reverse current.

Note: If the reverse bias voltage is continued to increase the PN-diode may get diode.

For Zener diode this case differs whenever the Vin in reverse bias is increased to the diode reverse breakdown voltage the output voltage is equal to Zener reverse breakdown voltage.

After this phenomenon, the diode produces avalanche current which means the current flowing is maximum. This mode is used for developing the power supply circuits.

VI characteristics:

By observing the VI characteristics the behavior of the PN-diode and zener diode can be easily understood.

PN-diode V-I characteristics:

PN- diode VI characteristics

                                                                       Fig 2: PN- diode VI characteristics

VI characteristics of zener diode

                                                                     Fig 3: VI characteristics of zener diode

From both V-I characteristics, the 1st quadrant is similar for PN and Zener diode. But the 3rd quadrant changes, when the PN- diode goes into avalanche breakdown the diode may get burnt or damaged. Whereas for Zener diode after avalanche breakdown it maintains a constant voltage with an increase in current (Iz).

Note: The reverse breakdown voltage for PN- diode is given in datasheet as VRRM.

Circuit designing:

            As from the previous description the Zener diode is placed in reverse biased and it is parallel to the Vin. which shown in below circuit. Here lets design a power supply using power supply using Zener diode. As in reverse biased mode after the Zener breakdown, the diode tries to draw maximum current from the source this may lead to destroying the diode. To protect it from the maximum current a source resistor is connected in series with the Zener diode to the power supply which is shown in below figure. The calculation of source resistor is given by the equation below

formula for finding source resistor

circuit diagram for zener voltage regulator

                                                           Fig 4: circuit diagram for zener voltage regulator.

Advantages:

  • It is a simple circuit to design
  • This requires 2 or 3 components for usage.
  • Providing high current capability.

Disadvantages:

  • The efficiency is poor for heavy loads because of power dissipation at series resistance and zener resistance with respective to load current.
  • Change in zener resistance changes the output voltage (Vo).
  • It is not suitable for larger current drawing loads, if connected the output voltage may decrease.
  • Here it is not possible to vary the output voltage.
Categories: posts, power supply

14 thoughts on “POWER SUPPLY DESIGN USING ZENER DIODE

  1. good information, nice post

  2. Hi. I see that you don’t update your page too often. I know that writing
    articles is time consuming and boring. But did you know that there is a tool that allows you to
    create new posts using existing content (from article directories or other
    blogs from your niche)? And it does it very well. The new articles are
    high quality and pass the copyscape test. Search
    in google and try: miftolo’s tools

  3. Good day! Do you use Twitter? I’d like to follow you if that would be ok.
    I’m undoubtedly enjoying your blog and look forward to new posts.

  4. Hi. I see that you don’t update your website too often.
    I know that writing posts is boring and time consuming.
    But did you know that there is a tool that allows you to
    create new posts using existing content (from article directories or other pages from
    your niche)? And it does it very well. The new posts are high quality and pass the copyscape test.
    Search in google and try: miftolo’s tools

  5. Wonderful blog you have here but I was wanting to know if you knew of any forums that cover the same topics discussed here? I’d really like to be a part of group where I can get opinions from other experienced individuals that share the same interest. If you have any recommendations, please let me know. Thanks a lot!

    1. You can find edaboard.com, engineersgarage.com, instructables on google, very soon we are also going to start such team support, thanks for being a part

  6. Magnificent site. Plenty of useful information here. I’m sending it to some friends ans additionally sharing in delicious. And certainly, thanks in your sweat! eekbdcedcabd

  7. Great website! I am loving it!! Will be back later to read some more. I am taking your feeds also kbgkeeekdfdf

  8. I think this is one of the most important info for me. And i am glad reading your article. But wanna remark on few general things, The web site style is ideal, the articles is really excellent D. Good job, cheers ddbddbdebgbdkkaf

  9. Wow! This could be one particular of the most useful blogs We’ve ever arrive across on this subject. Actually Excellent. I’m also an expert in this topic so I can understand your hard work. ecddedaeeefb

  10. Hey, thanks for the post.Really thank you! Really Cool. gckcefffdgge

  11. Very nice post. I certainly appreciate this website. ekagfbdddfeededb

  12. The power to run the optocoupler is supplied internally.You can decide whether you want to use the internal or external power supply by the use of software.

    1. Please post a clear question to understand properly. or send your design purpose.

Leave a Reply

Your email address will not be published. Required fields are marked *