Readers are advised to proceed with the construction of the presented circuits only after understanding the concepts from the core. Not adhering to this can lead to failures and frustrations.

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Sunday, April 1, 2012

How to Design a Power Supply Circuit - Simplest to the Most Complex

Whether it's an electronic noob or an expert engineer, all require this indispensable piece of equipment called the power supply unit. This is because no electronics can run without power, to be precise a low voltage DC power, and a power supply unit is a device which is specifically meant for fulfilling this purpose.

If this equipment is so important, it becomes imperative for all in the field to learn all the nitty-gritties of this important member of the electronic family.

Let's begin and learn how to design a power supply circuit, a simplest one first , probably for the noobs who would find this information extremely useful.

A power supply circuit will fundamentally require three main components for providing the intended results. A transformer, a diode and a capacitor.

The transformer is the device which has two sets of windings, one primary and the other one is the secondary. Mains 220v or 120v is fed to the primary winding which is transferred to the secondary winding to produce a lower induced voltage there.

The low stepped down voltage available at the secondary of the transformer is used for the intended application in electronic circuits, however before this secondary voltage can be used, it needs to be first rectified, meaning the voltage needs to be made into a DC first.

For example if the transfornmer secondary is rated at 12 volts then the acquired 12 volts from the transformer secondary will be a 12 volt AC acros the relevant wires.

Electronic circuit can never work with ACs and therefore this voltage should be transformed into a DC.

A diode is one device which effectively converts an AC to DC, there are three configurations through which basic power supply designs may be configured.

Using a single diode: The most basic and crude form of power supply design is the one which uses a single diode and a capacitor. Since a single diode will rectify only  one half cycle of the AC signal, this type of configuration requires a large output filter capacitor for compensating the above limitation.
A filter capacitor makes sure that after rectification, at the falling or decreasing sections of the resultant DC pattern, where the voltage tends to dip, these sections are filled and topped by the stored energy inside the capacitor.
The above compensation act done by the capacitors stored energy helps to maintain a clean and ripple free DC output which wouldn't be possible just by the diodes alone.


For a single diode power supply design, the transformer's secondary winding just needs to have a single winding with two ends.

However the above configuration cannot be considered an efficient power supply design due to its crude half wave rectification and limited output conditioning capabilities.

Using two diodes: Using a couple of diodes for making a power supply requires a transformer having a center tapped secondary winding. The diagram shows how the diodes are connected to the transformer.

Though, the two diodes work in tandem and tackle both the halves of the AC signal and produce a full wave rectification, the employed method is not efficient, because at any instant only one half winding of the transformer is utilized. This results in poor core saturation and unnecessary heating of the transformer, making this type of power supply configuration less efficient and an ordinary design.

Using four diodes: It's the best and universally accepted form of power supply configuration as far as the rectification process is concerned.
The clever use of four diodes makes things very simple, only a single secondary winding is all that is required, the core saturation is perfectly optimized resulting in an efficient AC to DC conversion. The figure shows how a full wave rectified power supply is made using four diodes and a relatively low value filter capacitor.

This type of diode configuration is popularly know as the bridge network, you may want to know how to construct a bridge rectifier, kindly refer to this article.

All the above power supply designs provide outputs with ordinary regulation and therefore cannot be considered perfect, these fail to provide ideal DC outputs, and therefore are not desirable for many sophisticated electronic circuits. Moreover these configurations does not include a variable voltage and current control features.

However the above features may be simply integrated to the above designs, rather with the last full wave power supply configuration through the introduction of a single IC and a few other passive components.

Using the IC 317: The IC LM 317 is a highly versatile device which is normally incorporated with power supplies for obtaining well regulated and variable voltage/current outputs. A few power supply example circuits using this IC is explained in this article.

Since the above IC can only support a maximum of 1.5 amps, for greater current outputs another similar device but with higher ratings may be used. The IC LM 338 works exactly like the LM 317 but is capable of handling up to 5 amps of current. A simple design is shown below.


For obtaining fixed voltage levels, 78XX series ICs may be employed with the above explained power supply circuits. The IC are comprehensively explained in this article.

Nowadays transformerless SMPS power supplies are becoming the favorites among the users, due to their high efficiency, high power delivering features at amazingly compact sizes.
Though building an SMPS power supply circuit at home is surely not for the novices in the field, engineers and enthusiasts with comprehensive knowledge about the subject can go about building such circuits at home.
A neat little switch mode power supply design has been discussed HERE.

There are a few other forms of power supplies which can be rather built by even the new electronic hobbyists and does not require transformers. Though very cheap and easy to build, these types of power supply circuits cannot support heavy current and are normally limited to 200 mA or so.

Two concepts of the above transformer less type of power supply circuits are discussed in the following couple of posts:

By Using High Voltage Capacitors,

By Using Hi -End ICs and FET

40 comments:

  1. sir can we use 78xx ic in d same circuit as u given for LM788 IC or we required some other value of capacitor and register for using 78XX in above circuit.....

    ReplyDelete
    Replies
    1. No you cannot replace a LM338 with 78XX IC, because they are entirely different with their specs and operations.

      Delete
  2. Sir I have a centre tap 12 v 0.5 amps transformer, what are the changes I need to make, I tried it with 4diode 1 diode circuit yu have posted , when I connect the 1000 muf 16v, The output is around 17-18 volts. What is the capcitor necessary and what changes I need to make for .5 amps 12v

    ReplyDelete
    Replies
    1. The voltage will usually rise after connecting a bridge and a capacitor, you cannot stop that.
      Normally once the load is connected the voltage gets restored to the rated level, however for extreme safety you may use a 7812 IC at the output, this will perfectly stabilize the output and provide an accurate 12V.

      Delete
  3. You are maintaining a very good blog. I like it. I was trying to make a 0-30V (3 Amp) variable power supply using IC 723. Facing issues with stability and current output. have worked with anything like this?

    ReplyDelete
    Replies
    1. Thank you!

      723 is a complicated IC to configure, the last circuit using LM338 is far better and easy to build than using IC723, so I would suggest to go for the last circuit shown in the above article.

      Delete
  4. WHEN CHARGING A 12V BATTERY HOW MUCH VOLTAGE FROM THE CHARGER IS REQUIRED TO CHARGER (MIN VOLTAGE TO PUSH POWER INTO THE BATT)

    ReplyDelete
    Replies
    1. Minimum voltage can be around 13.5v, but ideally it should be approximately 14.3V with a current rate of 1/10 battery AH.

      Delete
  5. how much can be outputted from LM338 IN TERMS OF VOLTAGE WHEN YOU IN PUT 17 VOLTS?

    ReplyDelete
  6. But sir i heard that....
    Capacitor did nt work on dc......
    Pls clear that....

    ReplyDelete
    Replies
    1. I did not understand your question, please make it clearer...

      Delete
  7. Hi Swagatam,

    How can i integrate the TIP36 to LM317 on this circuit? how it will be connected?

    i have a 9-0-9 30amps transformer.

    Regards,
    Mike

    ReplyDelete
    Replies
    1. Hi Mike,

      Please refer the article on TIP36, there you will find the circuit which shows how TIP36 can be connected with 7812 IC, you will have to replace the 7812 IC with a LM317 circuit.

      Regards.

      Delete
    2. Thanks Swagatam...

      i'm a avid fans of your blogsite.
      keep up and more power to you.

      Regards,
      Mike

      Delete
  8. hw to modify d ckt to so that i can giv 230/12v 1A transformer in the inpt to get 5v at the outpt???

    ReplyDelete
  9. sir, i need to design 50v,100v,150v dc power supplies for an actuator(stack piezo actuator whose maximum voltage is 150v).What should i do.I dont have any idea.Can u help me please?

    ReplyDelete
    Replies
    1. Using a small variac would be perhaps the best and safest option, other forms of circuits could be unsafe.

      Delete
  10. I think we can design these dc power supplies using a transformer,a bridge rectifier and a capacitor.

    But what should be the different voltage and current ratings of the transformer for designing the 50v,100v,150v dc power supplies?

    What should be the value and voltage rating of the capacitor?

    Can u help me by providing either the circuit diagrams of the power supply design using the transformer,bridge rectifier and capacitor for the 3 different dc power supplies of 50v,100v and 150v or by providing the links for getting the necessary materials,ciruit diagrams,equations for designing the 3 dc power supplies of 50v,100v and 150v.

    ReplyDelete
    Replies
    1. you may try out this circuit:

      http://www.gophoto.it/view.php?i=http://www.eleccircuit.com/wp-content/uploads/2012/07/the-variable-high-voltage-power-supply-0-300V.jpg

      Be sure to connect a 100 watt bulb in series with the input supply for safety, in case anything goes wrong...

      The circuit is NOT isolated from mains AC.

      Delete
    2. The transformer will not be required connect it directly to mains with a 100 watt bulb in series.

      Be extremely cautious as the entire circuit would be floating with mains high voltage.

      Delete
  11. which regulator IC to be used for 2 amps of output?

    ReplyDelete
  12. How do we decide the value of capacitor used?

    ReplyDelete
    Replies
    1. it's not critical, use highest possible value....

      Delete
  13. sir first of all congrats and thank you for running such a nice blog. Can you please tell me something about the analog group in power supply. only hint or any link will be also fine.

    ReplyDelete
    Replies
    1. Thanks you!

      you mean by using discrete transistors or mosfets??

      Delete
  14. Hello Sir,
    Day's Greet.

    I find this site is is very interesting and I like it very much.
    Sir,I am using LM2576 to get 5V.
    Input to the LM2576 should be minimum 7V.
    Max current handling capacity of LM2576 is 3A
    My transformer is 9V,1A.
    Load is 0.70A.
    What should be the value of capacitor.
    I got the value of load from DC power supply by providing 9V at the input of Bridge rectifier.
    Please, suggest the solution and its formula.

    Please reply me this here as well as on my email-id n_nogaja@yahoo.co.in

    ReplyDelete
    Replies
    1. You can refer to the following post, it explains the entire procedure of calculating filter capacitors in power supplies.

      http://www.tpub.com/neets/book7/27e.htm

      Delete
  15. thank you for everything sir.
    but I developed a 5v power supply, it works well but my worry is that the output current is to small so, how can I increase it thank you.

    ReplyDelete
    Replies
    1. The output current will depend on the transformer rating....if you have used a 7805 IC the transformer could be rated at 1 ampere.

      Delete
  16. Thanks for the article.
    I need to step-up 8V(p-p) 1MHz AC signal,which type of transformer should I use?

    ReplyDelete
    Replies
    1. you will need a ferrite ring type of transformer for this.

      Delete
    2. Sir please can u give more details on this? and is it easily available? I require it on urgent basis.

      Delete
    3. you can try a joule thief circuit kind of configuration for your application.
      you will find plenty of such designs on the web.

      Delete
    4. Thank you sir for the reply.
      Sir,on the receiver side I'm getting enough voltage but very low current.I need to amplify current but at the same time voltage should not drop more than 1V.How can I do that?

      Delete
    5. which circuit you have used, pls provide me the link.

      Delete

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