220VAC to 5VDC transformator?

I have a beginner question.

If i want to make my own circuit that takes 220VAC to 5VDC that delivers around 2 ampere. How can i make that the simplest way without burning my house down?

I thinking an 220VAC to 12ish VAC transformator followed by four rectifier diodes and one or two big condencators for converting it to DC, and a simple buck converter at the end that takes the remaining voltage and converts it to 5V.

Is that right?

That would work. Or get a €5 230VAC to 5VDC switching power supply module.
Alright, China is out of the question perhaps due to tax issues. Then make it €15 and source it from Europe. Probably still cheaper than a transformer +buck + components and certainly smaller/less copper & iron needed.

Okay thanks.

But if the transformator outputs lets say 26VAC and i want 5VDC out and 2 ampere. Can i use some standard in4001 diodes as rectifier? Can i draw 2 amps through them?

Hi @Bjerknez .

For your questions and so that you don't set your house on fire, I suggest you take at least one basic electricity/electronics course.

Here I made a mistake in the way I wrote:
"For your questions"
Understand it this way:
"From the questions you asked I realized that he has no knowledge of basic electrics" .......

RV mineirin

I do not need any course for asking question do i?

Just take responsibility for what you answer, and i will take responsibility for my life, and my house.

If i ask someone how to cut a tree. It doesent mean i'm going to cut my head of with a chain saw.

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Thrift stores, garage sales, etc. have boxes of used but fully functional, safety validated power bricks for cameras, cell phones, laptops, monitors, etc.

Find one that runs on 220VAC and outputs 5V at 2A. It should cost less than a cup of cappuccino.

I thinking an 220VAC to 12ish VAC transformator

Think "5ish". The peak aC voltage is 1.4 times the RMS voltage.

1n4001 will be on the edge if its ratings, so not a good idea.
If the secondary VAC is 26 V you obviously don't need to run 2A through them given your 5V@2A output after the buck converter. Different story if you use a linear regulator, but then you'd need a hell of a heat sink as well.

@ruilviana has a point btw. You're going to deal with 230VAC at least on the primary side and that means you need to know what you're doing. Whatever you do, please be very careful. 230V can kill, burn your house down and a glass fuse can explode if you wire a switch wrong throwing glass splinters into your eyes.

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So if the output is 5V and 2amp (10 watt) the ampere through diodes are smaller because of the higher voltage? Or am i thinking wrong?

And yes, i am aware of all the hassards regards to this. I just ask questions. What i'm going to do with my answers is MY responsibility.

I meant if the ampere out is 2 amp, then the ampere through diodes is around 400mA? (26VDC x 0.4) is around 10W. ?

If the power supply delivers 2A, that is the average current through the rectifier diodes. Take into account the approximately 1V forward voltage drop of each diode at that current.

If a switching buck converter is used to reduce the output of the rectifier/filter, then the current will be less.

Thanks. That answered my question :slight_smile:

Yes, about 400mA on average. Peak currents will be higher, but a 1n400x would survive those. Btw I prefer to use 1uf4007's to reduce switching noise a bit. They're also good for up to 1000V, which makes them convenient to have around.

I don't think the 1N4004 will cut it. You haven't specified what capacitor you might be using but if it 1000µF (or maybe less) when you plug in the transformer there will be a large current spike to charge the capacitor (which is assumedly at 0 volts).

In addition, (again depending on you input capacitor(s)) the diodes will conduct only during the top 20° or so. Meaning your diode current will have to be enough to pass the energy you need when only conducting for a short period of the mains cycle.

I understand, however this group gets a lot of questions from folks who don't know how dangerous working with mains is. So most of us attempt to make sure we don't encourage dangerous projects by limiting the information we provide.

I agree. Really you should be using 3A rectifiers. Seriously - don't risk using 1N400n rectifiers for a 2A power supply, they have a rating of 1A "average forward current".

I can't say for sure as we don't know the transformer or storage capacitors.

But at a 2A DC output, if the diodes are only conducting 50% of the time then they diode current is approx 4Amps.

If conduction time is less then the current through the diode is larger.


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3A rectifiers are so cheap, it's a no-brainer.

Hmmm, well ...

Frankly, considering the current state of affairs, that really is an unproductive approach. :woozy_face:

Whatever I may have done in the past - and I have (built power supplies) but it was a long time ago - this is simply no longer a viable approach.

As you will find in all consumer appliances, switchmode power supplies have taken over and for very good reasons. They are efficient, they are small and lightweight and now they are cheap. The bulky mains transformer is now more expensive than the sum of components in the switchmode supply.

So you do not start with a mains transformer, you use a switchmode supply from input to output. But the design of switchmode supplies is anything but trivial and it is extremely inadvisable to even consider it without considerable electronics engineering experience.

I suggest this project is a "dead duck". What you actually need is readily available and quite cheap. Possibly even cheaper second-hand from the "thrift" store. Have fun with the mental exercise here, but don't try it in practice. :grin:

You can buy ready-to-go 5V 2A power supplies and USB chargers in China or EU for less than the cost of your rectifier diodes. Just make sure that your power supply is galvanically isolated if you use a switching power supply. Some of them don't use an insulation transformer.
Anything you buy should have the CE mark and isolation class 2 or better.

WOW... I did'nt know that..... :yawning_face:

I think i can buy anything that is ready made. So what is the point asking inn here? I'm here to learn new things, not to buy ready made stuff.

Learning by doing (and asking) is a good thing. As said earlier: Do not worry about my life and my house. I take care of that. If you are against my method to do circuits, it's better to not post anything. Are you really conserned, send me an PM and not clutter up the threads.