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Designing Power Supply Circuit – Simplest to the Most Complex

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The post details how to design and build a good work bench power supply circuit right from the basic design to the reasonably sophisticated power supply having extended features.

Designing a Workbench Power Supply is Indispensable

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 basic 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.

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 or LM338:

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

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 78XX ICs are comprehensively explained for your refernce

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.

You can also learn about a  neat little switch mode power supply design.

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.

Transformerless Power Supply Design

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

Feedback from One of the Dedicated Readers of this Blog

Dear Swagatam Majumdar,

I wish to make a psu for a micro-controller and its dependent components...

I want to get a stable +5V out and +3.3V out from the psu, I'm not sure of the amp-age but I think a 5A total should be enough, there will also be 5V Mouse and 5V Keyboard and 3 x SN74HC595 IC's too and 2 x 512Kb SRAM ... So I really dont know the amp-age to aim for....

I guess 5Amp is enough?.... My MAIN question is which TRANSFORMER to use and which DIODES to use? I have chosen The transformer after reading somewhere online that the bridge rectifier cause a VOLT DROP of 1.4V in general and in your blog above you state the bridge recitfier will cause the voltage to go up?...

SO I am unsure (I am unsure anyway being new to electronics) ..... The FIRST transformer I chose was this one. Please advise me which one is BEST for my needs and which DIODES to use too.... I would like to use the PSU for a board very similar to this....

Please help and guide me the best way to make a suitable MAINS 220/240V PSU which gives me STABLE 5V and 3.3V for use with my design. Thank You In Advance.

How to Get Constant 5V, and 3V from Power Supply Circuit

Hello, you can achieve that simply through a 7805 IC for getting the 5V and by adding a couple 1N4007 diodes to this 5V for getting approximately 3.3V.

5 amp looks too high and I don't think you would require this much high current unless you are also using this supply with an external driver stage carrying higher loads such as a high watt LED or a motor etc.

so I am sure that your requirement can be easily fulfilled through the above mentioned procedures.

for powering MCU through the above procedure you can use a 0-9V or a 0-12V trafo with 1amp current, diodes could be 1N4007 x 4nos

The diodes will drop 1.4V when the input is a DC but when it's an AC like from a trafo then the output will be raised by a factor of 1.21.

make sure to use a 2200uF / 25V cap after the bridge for the filtration

I hope the info will enlighten you and answer your queries.

The following image shows how to get 5V and 3.3V constant from a given power supply circuit.

Making a Fixed 12V Regulator Circuit

In the above diagram we can see how an ordinary 7805 regulator IC could be used for creating a fixed 5V regulated output.

In case you wanted to achieve a fixed 12V regulated power supply, the same configuration could be applied for getting the required results, as shown below:

 

12V regulated power supply circuit using LM7812 IC

12V, 5V Regulated Power supply

Now suppose you had circuit applications which needed a dual supply in the range of 12V fixed and also 5V fixed regulated supplies.

For such applications the above discussed design could be simply modified by using a 7812 IC and then subsequently a 7805 IC for getting the required 12V and 5V regulated power supply output together, as indicated below:

 

12, 5V regulated power supply circuit using IC 7812 and IC 7805






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Comments

  1. Hi Swagatam! My question relates to using two 12vdc 1A power supplies in series to produce 24vdc. I recently received two a 5m reel of 24v 2835 strip LEDs by mistake. I am trying to figure out how I may use these as I only have 12v power supplies. It may be worth the money to purchase a 24v power supply, rather than discarding the two 5m reels. I may use these in small strips so as to not require large power supplies. If you have any ideas as to how I can use these 24v LED reels, please share them with me. Thanks!

    Reply

    • Hi Norman, the only easy option is to make a boost converter circuit and use the LED with it.

      you can try the last circuit from this link

      https://homemade-circuits.com/2014/11/12v-car-laptop-charger-circuit-using.html

      the T1 feedback is not crucial, it can be eliminated….

      Reply

  3. Sir,

    Hoping you maybe able to assist with an issue with a power supply on a pre-amp.
    The pre-amp has been upgraded several times and along with it the power supply, originally it had 4 small capacitors each 1000 uf then they were replaced with 1,000uf x 100v and the toroid was replaced with a 600va x 71/0/71…every thing worked well for 8 years until last weekend until I decided to upgrade the capacitors to 6,800uf each (two each feed), they slotted in just perfect and when switched on was just excellent, every thing was just spot on i.e. 71/0/71 ac in and 90/0/90dc to the main board on the board sits 4 little Nu-Vista valves hence the 90volt output…….I then connected the power supply to the main board and switched on and BANG..the tracks from the A/C input on both had been taken out thro the 3 filter caps (104j x 250v) and only up to the rectifier (W04M 1.5amp) everything else was fine…put the P/S back as it was and the pre-amp works just fine…….Question, what went wrong?…too much capacitance or as I feel the rectifier needs beefing up as the other was small and only 1.5amp…oh and between the main caps are two resistors 330 ohm 2 watts metal film +/- 1%

    Your input with this would be greatly appreciated

    Mick

    Reply

    • Hi Mick, It can be difficult to judge precisely without seeing the damaged area practically, yes increasing the capacitor value could have caused this due to an increase in the current level, and if the tracks got burnt then certainly something across these tracks could not handle the current generated from the 6800uF cap.

      the 330 ohms are no match for 91V, even though these are rated at 2 watt still these would begin smoking at 91V….but tracks getting burnt is strange unless something shorted them across the supply rails…you will need to find the weak link between these tracks which might have triggered the issue.

      Reply

    • Hi, again…I could send you images, the tracks destroyed go from AC in to the rectifier and no further….getting a bigger rectifier tomorrow so we shall see, nothing has changed over the past 8 years apart from these new caps, the only thing that was between the rectifier and AC in were three 104J x 250 volt caps for I assume smoothing…..will get back to you in a few days and let you know which part of my house wall is still standing….many thanks for your time

      Mick

      Reply

    • I have seen the images, according to me the bridge rectifier is the culprit, may be it was not rated to handle 91V and the increased current and as a result it burnt….because rest of the components look OK, so that clearly indicates that the issue is with the bridge.

      Reply

  4. Sir, I want to build a sterio amplifier using IC LM3886 two no. Purchase power supply ready board low ESR using 4700×8 cap in dual rail.( I.e. + and – ). I am getting a 50hz noise. Transformer using 18-0-18 3A. I deside to use a load resistance, but the value how to calculate? Will u suggest to replace the transformer? (As the transformer become very hot within short period.) Circuit I have purchased from eightaudio.com. they suggest to use 22-0-22 4A transformer. Please help me.

    Reply

    • Jyotirmoy, you will need to install the entire amplifier board and the power supply transformer inside a good metal cabinet, once this is done the 50Hz ripple will be significantly reduced.

      Make sure to connect your amplifier negative line with the metal box, and also make sure the transformer is tightly clamped with the box using nuts and bolts.

      If your transformer is becoming HOT then it's not rated correctly or is of bad quality, replace it with a new one as per the recommended specifications of the amplifier and use a good quality transformer from a standard manufacturer.

      Reply

  5. gud day sir, i build a 0-30v variable psu w/ 3amp transformer and the output is 0-24v i also used of kbp206 bridge rectifier and IC Lm317T but when i adjusting VR the voltages is only 19.++v..i wonder some of the circuit in the other blog are the same compare to your blog that used of LM338 instead of LM317T. in my parts writing above and the voltages only reach in 19.-v, what do you think for this. have a relation with the used of LM317 instead of LM338?

    Reply

  7. Good day thanks so much for your kindness in sending us the circuit. But please I have some questions first can we design the power supply of the sound decibel meter circuit using a centre tapped transformer, secondly we want to use buzzers and incandescent lamps for the design instead using only LEDs. Reason is that we want to draw students attention with buzzer and lamp when the noise level in the classroom is high. Regards

    Reply

    • you can use a center tap transformer for powering the circuit, as shown in the second circuit above.

      and you can easily reparable the LEDs with 12V piezo buzzers for the relevant indications.

      Reply

    • Zunair, No, it's not possible in the LM338 circuit, you can use it with a different configuration if you intend to achieve a fixed 5V from it.

      Reply

  10. Hello swagatam,i'm using 7805 regulator in my power supply. Which diodes should i use, and how to decide the specifications of capacitor that need to be used for getting 5V output.

    Reply

  11. Good day, sir.
    It was mentioned that, in PS circuit designs without ICs, the outputs have “ordinary regulation” and “fail to provide ideal DC output”. Can you please elaborate? Also, does this mean that, when viewed using an oscilloscope, the output voltage is not linear (specifically, horizontal)?
    I have been wondering about this for hours and my teacher won't answer me. It would be great to know about some enlightenment. 🙂

    Reply

    • Good day Chritian,

      regulation refers to voltage and current being constant, but the level of pureness of the DC is governed by the filter capacitor not by the IC….therefore the cleaning the DC is done by the filter cap while the ICs make sure that the voltage and the current remain steady all throughout regardless of the input fluctuations.

      the straightness of the DC horizontal line is essentially controlled by the filter capacitor

      Reply

  12. Namaste Swagatam,

    https://homemade-circuits.com/2012/03/how-to-design-power-supply-simplest-to.html

    In the first diagram in above article, you show a HALF WAVE rectifier, yet the diagram says FULL WAVE.

    You need to fix that if you want to teach and not confuse!

    Have a nice day!
    Jeff

    Reply

    • Hello Ashok, it's to channelize both positive and the negative half cycles of the AC into only positive cycles….thus the negative and the positive cycles both are converted to positive cycles.

      Reply

  15. Dear sir,
    I have made one development board of Pic18f4520 Microcontroller. And now i need to provide it exact 5 volt dc power supply. Please help me in designing power supply. What should i do?

    Reply

    • Thanks Sayli,

      If you want to build an SMPS type of power supply then you can try the following design:

      https://homemade-circuits.com/2012/03/how-to-make-simple-12-v-1-amp-switch.html

      for a transformer power supply you can simply use a 0-12V transformer and join a bridge rectifier with a filter capacitor, as shown in the third diagram above for getting a 15V output

      Reply

    • there is a formula for it, however practically it's never required because most electronic circuits will work nicely even if there's a slight ripple….but as a rule of thumb it's recommended to use a value that may be as high as possible from the user, because the degree of filtration is directly proportional to the value of the cap (uF)

      Reply

  19. SIR in one interview someone ask me about the RC time constant in designing of POWER SUPPLY what value of capacitor to use how u calculate this much value is required ? please answer

    Reply

    • RC time constant has no relevance to a power supply, if you are referring to the filter capacitor formula you can easily find it online, just type: "power supply filter capacitor formula" you'll find many related sources

      Reply

  21. Hello sir,
    what do you think about adding non-polar caps in parallel to each diode in the bridge network configuration? do these guys provide better stability??
    Do you suggest me connecting a resistor at the output after the electrolytic cap?
    does connecting resistor reduce hum on the DC output.
    Please help in such thoughts.

    Reply

    • Hello Sherwin, such enhancements are not crucial and may be ignored, because the circuits which would be operated using these supplies would be already sophisticated enough to tackle such small inefficiencies from the power supply.

      Reply

  24. 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

    Reply

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

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

      Reply

  25. 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.

    Reply

  28. 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.

    Reply

    • you may try out this circuit:

      www.gophoto.it/view.php?i=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.

      Reply

    • 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.

      Reply

  29. 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?

    Reply

  32. 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

    Reply

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

    Reply

  36. 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?

    Reply

    • 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.

      Reply

  37. 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

    Reply

    • 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.

      Reply

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