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The Simplest Power Supply Circuit

By 34 Comments

power-supply-protoboardThis power supply circuit is easy to build and cheap. And it requires only 5 components.

I have built many circuits in my life, but this is actually the first time I’ve built a power supply circuit from scratch.

The final project I wanted to build was a wall adapter with a USB socket to charge my iPhone. But first I wanted to start by creating a simple circuit that converts from the main power voltage, 220V or 110V, to 5V.

As I’m in Australia while writing this, and the voltage here is 220V, I built this with 220V in mind. But it’s very easy to convert to 110V instead by switching one connection (or one component).

Caution: Do NOT connect anything you make yourself to the power mains if you are not 100% sure about what you are doing. Doing it wrong can cause serious damage, even death. Use the information provided here at your own risk.

If you want a perfectly safe and extremely useful power supply circuit, you should check out this portable USB charger that I built. It even includes a downloadable step-by-step tutorial on how to build it yourself.

Designing The Power Supply

I want to base the power supply circuit around the LM7805 voltage regulator because it’s an easy-to-find chip that is simple to use. This component will give a stable output voltage of 5V up to 1.5 A.

I can easily figure out how to use the LM7805 by looking in its datasheet.

From the datasheet I found this little circuit:

Power supply circuit from lm7805 datasheet

Choosing Capacitor Values

The above image shows the voltage regulator with a 0.33 µF capacitor on the input and a 0.1 µF on the output. It’s hard to find a good source of info on these capacitor values, but according to this Q&A there’s nothing magically about these values.

There are a lot of opinions on the web around these capacitors. Some suggest 0.1 µF capacitors, others suggest 100 µF capacitors. And some suggest using both a 0.1 µF and a 100 µF in parallel.

The values you should use depends on a lot of factors. For example how long the wires are going to be. But this article is about how to build a simple power supply circuit, so let’s not complicate things. Probably, almost any capacitor value will work. It will probably even work without capacitors.

For the sake of making the output voltage “a little bit stable”, I’m going to use a 1 µF capacitor on the output. I’ll skip the input capacitor, because there will be a capacitor in this position anyway – just keep reading.

Converting From 220V

The datasheet also says that it needs between 7V and 25V to work correctly. So, I only need to add a few components that convert 220V (or 110V) AC to a DC voltage that stays between 7V and 25V.

This is relatively easy. I’ll just add a transformer that transforms the voltage down to for example around 12V. Then I’ll feed this AC voltage into a bridge rectifier to rectify it.

And I’ll use a large capacitor on the output to keep the voltage above the necessary 7V at all times. This capacitor value isn’t critical. I’ve seen many power supply circuit designs that use 470 or 1000 µF, so I’ll try with 470 µF for now.

The Power Supply Circuit Diagram

So, the final circuit looks like this:

basic-power-supply-circuit-2

Parts List

Part Value Description
T1 220V (or 110V) to 12V Transformer
DB1 Diode Bridge Rectifier
C1 470 µF (20V and upwards) Capacitor
C2 1 µF (10V and upwards) Capacitor
U1 7805 Voltage Regulator

The total cost of the components is about $12-15. The most expensive component is the transformer (about $10).

Finding Components For The Circuit

When I’m not sure how to choose components for a circuit, I usually go to online electronics stores for hobbyists and look at their options. These stores usually stock components that should work in a standard power supply without any special requirements.

In Australia, Jaycar is a nice option.

A quick search on “transformer” on Jaycar gives me several options. The input voltage needs to be around 220V and the output around 12V. After a quick scan of their options and prices, I decided on this one:
https://www.jaycar.com.au/12-6v-ct-7va-500ma-centre-tapped-type-2853-transformer/p/MM2013

The transformer has a center tap on the output side which I can ignore.

This one is for 220V. If you live in a country with 110V the stores in your country will probably have the correct version for you. Click here to check out my list of online stores.

Then I need a rectifier. We can use 4 power diodes (ex 1N4007), or a bridge rectifier (which is basically four diodes built into one component). The cheapest option that pops up when searching for a bridge rectifier on Jaycar is this one:
https://www.jaycar.com.au/w04-1-5a-400v-bridge-rectifier/p/ZR1304

power-supply-components

The Finished Circuit

This is an easy circuit to solder onto a prototyping board. Here’s the prototype I built:

power-supply-protoboard

5v-power-supply-circuit-working

Reminder: Do not connect anything you build yourself to the power mains unless you are 100% sure about what you are doing. Use the information provided here at your own risk.

Did You Build It?

Did you build this circuit? What’s your experience? Anything you struggled with? Let me know in the comments below how it went.


Reader Interactions

Comments

  2. When I search on google for a 110 v transformer, the results are always for power supplies
    rather than just transformers.

    Can you please offer a suggestion for a suitable transformer in US ?

    Reply

  3. I have not built this circuit. But two months ago I built a mobile charger that works on any smart phone including apple ipods, iphones & ipads. I used am LM7805 with one USB type A connector & four resistors wgich is required to charge any apple ipod, iphone & ipad. It also charges any other brands of smart phone. I have tested it on friends mobile phones & those that have ipads or other tablets. They can’t believe that my cost is way cheaper than any apple chargers. I don’t use any transformer as I have designed it to use Solar panels (12V 10W to 200W) or any wall charger ACDC from 9V upwards. I have also bulit a Variable power suppky from 1.2V to 22V using LM317T regulator.

    Reply

  4. I have an old van that I would like to install this in. Since the vehicles in the u.s. run on 12 volts I wouldn’t need a Transformer but probably should use the full wave rectifier. Any ideas?

    Reply

    • Hi,

      You’re right. In this case, you wouldn’t need a transformer. But the 12V is already a DC voltage, so you wouldn’t need the rectifier either.

      I would use the capacitors, for stability’s sake. But don’t worry too much about the exact values.

      Best,
      Oyvind

      Reply

  5. I have build power supply alot for my projects, what I find fascinating about it the pieces you put together to get your stabilised dc from your ac. At it was a challenge, because any reversing of components like bridge rectifier diode, capacitor polarity will render a fault it… Thus details need to paid

    Building power supply is quite fundamental for any electronic hobbyist, yet its a do or die skill that one need to have, cuz it set that freedom to manipulate power supply. Oyvind your application of electronic here is remarkable, it just show how cost effective it is to hve such a skill.

    A challenge I wanna take t my side is building an inverter, a device for converting Dc to Ac.

    FIngertips Electronics
    Chris

    Reply

  6. Mains Wiring:
    I think it is very irresponsible of you to post this, and to be embacking on building a mobile phone charger. Clearly, you don’t know what you’re doing “…but this is actually the first time I’ve built a power supply circuit from scratch.” If you actually knew what you were doing, you wouldn’t be saying “Caution: Do NOT connect anything you make yourself to the power mains if you are not 100% sure about what you are doing.”

    You would instead be posting a detailed description of the things you need to know and do when working with mains power. Like securely mounting components on proper chassis, including a fuse on the mains side of the transformer, using a double pole switch so that you know that you aways switch line and neutral together. In Australia, evey power point has a earth pin. So you make sure that the metal chassis and cabinet are earthed. And you do use a metal cabinet. If there is some sort of failure that results in a live wire coming in contact with the cabinet, the current goes to earth and the fuse blows.

    If you use a plastic case with externally exposed metal parts – think mounting screw heads – you’ve made a death trap.

    I could go on. The photo of a multimeter with probe tips near a mains circuit is quite horrifying.

    People don’t go around intentionally electrocuting themselves or setting things on fire with their mains powered projects. They just don’t know how to approach this stuff safely. The probes and alligator clips on the $9 Jaycar multimeter are an accident waiting to happen.

    Lithium Batteries:
    Lithium chemistry batteries are dangerous. Period. I don’t need to explain this, just look at this link
    .
    Odds are Samsung’s current problems are something to do with their batteries or their battery management circuits. If you really want to make a phone charger for yourself, read this application note from Microchip: http://ww1.microchip.com/downloads/en/AppNotes/00947a.pdf.

    It explains everything that needs to happen when charging lithium batteries and includes a simple circuit diagram for a charger that is managed by one of their charge controller chips.

    Please do some research before you start posting stuff on the Internet. I you start with how to
    safely construct a mains powered device of any kind.

    Reply

  7. OK, So your comment software killed the link. Plug this into Google:
    third-party batteries site:www.howtogeek.com
    The first link that comes up tells the story.

    Reply

  9. Well for me that was probably harsh Russell, i understand the fact that safety must not be neglected in whatever we do but i also know that there are better ways to say that. Thanks at Oyvind.

    Reply

  10. Thanks for the information, seems like a really good project. Do you have any suggestions on how to build a variable power supply, say 5 – 24 volts. I believe it would be so much cheaper to build one then to buy one. Your help will be appreciated Oyvind

    Reply

  12. I need a 24 Volt DC output supply as charger for my Sanyo Enacle power-assist bike as I do not actually have the original charger when I bought this second hand bike from surplus store. I want to build the needed charger myself by using 3A center-tap 24 V output xformer, question is: do I need to have the same (value) component mentioned above with this 24 VDC output or will it matter? If so, can you email me the simple schematic diagram and the component value in building 24 VDC regulated output charger by using 3A Xformer (12-0-12).

    Reply

    • You need a different voltage regulator than the one in this diagram. A quick search gave me the 7824 chip as an option. Look in it’s datasheet to learn about it. You can probably use the same value for the other components.

      Best,
      Oyvind

      Reply

  14. Hi Oyvind!
    I’m going to make a circuit that use Arduino to control 5 solenoid valve 12VDC and 2 motor 12VDC.
    My problem is that my adapter 220VAC – 12VAC can’t supply enough power for these 7 things.
    I wonder should I reuse my old ATX power supply of PC or build a new one.
    Can you suggest what I should do?
    Thanks,
    TADT.

    Reply

  15. Thank you for giving me the opportunity to visit this impressive website. There is plenty of valuable info listed on this site.
    I have seen a lot of tricks. It is too much to absorb at once, thus I definitely will return to view more.

    Reply

  16. Hi Oyvind. Can u suggest a safest xforless pwr supply that can give an sdjustable output of 1.2 to 50V DC on a 230V/ 60Hertz input
    Thanks,
    Ding (i am an avid follower of yours from the Manila)

    Reply

  18. Sir I have a a printer’s power supply 32v I have an amplifier circuit board it requires 12v 3amp power supply., so guide me how to reduce 32v to 12v supply

    Reply

  19. Hello. im kinda new into electronics, can you explain why you choose 470uf capacitor in that circuit. i understand the part in the 20V because its the Max. voltage it can store, i just want to know why you choose 470uf

    thanks you

    Reply

    • The 20V is the maximum voltage drop it can have without the risk of damaging it.

      It’s the 470µF that tells you about its ability to store energy. The larger, the more energy it can store.

      Reply

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