220VAC to 5VDC (Compact)

Hey there,

I want to design a circuit, which requires 220VAC to be converted to 5VDC to power the digital logic. The main target is to make the circuit as small as possible, while maintaining a reasonable price for the assembly.

The first idea was to use a 220V/6V transformer with a full bridge rectifier and linear regulator (L7805CV), but the transformer is so huge, I start to think that I have made a wrong choice there.

What would you recommend to transform 220VAC to 5VDC to save maximum space, while keeping it not as expensive?

The current draw from 5VDC source would be 200mA at maximum, varying load.

Thank you

What would you recommend to transform 220VAC to 5VDC to save maximum space, while keeping it not as expensive?

I'd recommend buying a ready made power supply. Or, you could do what I do which is I collect wall worts from old electronic kit that is being discarded and keep them, as a result I never need to buy a mains power supply for my projects; I have loads of them.

Designing your own, let alone designing your own and making it really small and cheap, would be a near impossible task.

PerryBebbington: Or, you could do what I do which is I collect wall worts from old electronic kit that is being discarded and keep them, as a result I never need to buy a mains power supply for my projects; I have loads of them.

I used to but linear/transformer PS's use/waste power ALL the time and are usually less than 70% efficient when you do draw power from one.

I threw 2 boxes of the things out when I could have spent nights recovering winding wire.

If the wall wart is heavy, replace it if you still use it. Switching power supplies have been the way to go since the 80's.

I have $2 phone chargers that deliver 5V up to 500mA. They price so low in the 10's of millions.

I see a misunderstanding here and I might be at fault for it.

This question appeared, because I want to design a pluggable wall plug, which basically turns any wall plug into a IR remote controllable wall plug. For this I have decided to use a 5VDC relay and an Atmega8, which both need 5 volts, and the current draw of these components is little, it will probably never go over 200mA.

And since here locally electronic hobbyism isn't a very popular thing, alot of circuits must be ordered from the internet and I have to wait for a month or two to get them, hence why I would rather take the time to solder one myself.

So I am trying to come up with a solution on how can I get a very space-friendly Mains>5VDC power supply to combine into my general circuit with the atmega and relay, a seperate wall wart would not be the solution.

Also, nothing bad about the linear regulator since it doesnt conduct decent power and has very friendly 6V at input, energy efficiency is not that important in this case

https://drive.google.com/file/d/1XmaUhcyo75YXANbbimCt9PESVT0KY4lC/view?usp=sharing

Here you can see the one converter I already made, but the transformer is a bit too big

IR remote controllable wall plug have been sold on the market for years. They are also small. Building Mains to 5V supplies since the 1970:s I now wellcome those ready made, small, reliable, and in the final end, cheaper ready made stuff.

GoForSmoke: I used to but linear/transformer PS's use/waste power ALL the time and are usually less than 70% efficient when you do draw power from one.

I'm not sure what your point is, I only have ones with switching converters in, not ones with mains transformers.

I am trying to come up with a solution on how can I get a very space-friendly Mains>5VDC power supply to combine into my general circuit with the atmega and relay, a separate wall wart would not be the solution.

The extra background is useful but it does not change the fact that designing such a thing is a big, difficult task. Switch mode power supplies are not easy to design, small mains powered ones even less easy. The manufacturers have expert designers and money to spend, which then can then recover across millions of units sold. I could possibly suggest you copy an existing design, but if I were to do that I'd have to caution you against intellectual property theft, so I won't make any such suggestions.

That said, chip manufacturers usually put reference designs in their data sheets, which you are, of course, welcome to use.

How many do you need anyway? If only a small number then removing the guts from a wall wart and using it in your project is still an option.

I want to design a pluggable wall plug, which basically turns any wall plug into a IR remote controllable wall plug.

If you are posting on this forum for advice, there is no chance at all that you can do this safely.

Leave this to professionals and buy an IR or RF controlled remote switch. They have been available for at least 50 years.

Here you can see the one converter I already made, but the transformer is a bit too big

Since it works at higher frequency, the transformer for a switching power supply can be smaller & lighter.

But as everybody is saying, it's not easy (or cheap) to design & build your own. And just in general, the smaller you make stuff, the harder it is to build "at home".

For small transformers, search for “control transformer”. Perhaps line these on Ebay..

Paul

Just my 2 cents....

The first idea was to use a 220V/6V transformer

If I am correct, that would be a 36.6666... to 1 transformer. That requires a lot of winding on the primary side, very few windings on the secondary side.

A 10:1 transformer would be a lot less windings on the primary side, making it smaller. The first datasheet I looked at for a LM78xx voltage regulator said max input voltage to be 35v. Here's the datasheet: http://ee-classes.usc.edu/ee459/library/datasheets/LM7805.pdf

A 10:1 transformer will give you 22 volts to the voltage regulator. Of course, your rectifier will have to handle that voltage as well.

And since here locally electronic hobbyism isn't a very popular thing, alot of circuits must be ordered from the internet and I have to wait for a month or two to get them, hence why I would rather take the time to solder one myself.

Given the time it might take for you to get parts, you might consider tearing apart a wall tranformer/usb charger. They are digital switching power supplies and they are almost free. Most are thrown away because the wire/connector fail, but the power supply still works....

Randy

Yes scavenge a small switch mode supply that does what you want and then just put the IR interface on the low voltage side. Without surface mount components your footprint will be big to say nothing of the safety issues already mentioned.

Zengit: I see a misunderstanding here and I might be at fault for it.

This question appeared, because I want to design a pluggable wall plug, which basically turns any wall plug into a IR remote controllable wall plug. For this I have decided to use a 5VDC relay and an Atmega8, which both need 5 volts, and the current draw of these components is little, it will probably never go over 200mA.

You can make your own converter after a lot of research after reading a lot of tutorials. What is out there patented, made by engineers is likely to be beyond your easy reach so USE what is.

Make something that can plug into the average USB/phone charger. Give it IR read (what, no wifi?) and transistor-not-relay to switch power. Find out how much 5V it takes to switch a coil and magnet relay, external power is needed for relays.

Learn about FETs (field effect transistors) as they're more efficient either full ON or full OFF. Logic level FETs can be switched with 5V, if you buy in tens you can get them pretty cheap. Save relays for switching AC power.

DVDdoug: Since it works at higher frequency, the transformer for a switching power supply can be smaller & lighter.

But as everybody is saying, it's not easy (or cheap) to design & build your own. And just in general, the smaller you make stuff, the harder it is to build "at home".

What transformer? Switchers use transistors.

Instead of DIY, why don't you try a 220v european USB wall charger like below. You could even hang an arduino or a wifi board off of it.

https://www.ebay.com/itm/3-USB-Solid-Charger-European-Regulations-US-Travel-Mobile-Phone-Charging-Head/274043780531?hash=item3fce483db3:m:msNQjviqb3YiLPHd2m1tYYQ

Thank you all for your answers.

jremington:
If you are posting on this forum for advice, there is no chance at all that you can do this safely.

Regarding safety suggestions: I have already done this several times and am always cautious with 220VAC, I take into consideration component power ratings and not touch any wires when the circuit is plugged into mains, but thank you for your concern.

The conclusion: A 220v/6v transformer with linear regulator is a good and easy solution to get 5VDC in general, but it takes alot of space due to the huge amount of windings due to the big transformation coefficient. To save space, modern converters use transformers with smaller transformation coefficient (220v/22v f.e.), but with such a high voltage difference linear regulators can be thrown into the trashbin and a switching power supply must be made, and that is where the task gets nearly impossible for a hobbyist.

The best option for me seems to be scavenging the guts of phone chargers and fixing them on my general circuit.

Paul_KD7HB:
For small transformers, search for “control transformer”. Perhaps line these on Ebay..

This could also be a solution, but an expensive one.

GoForSmoke:
Learn about FETs (field effect transistors) as they’re more efficient either full ON or full OFF. Logic level FETs can be switched with 5V, if you buy in tens you can get them pretty cheap. Save relays for switching AC power.

Use a mosfet to conduct AC current to home appliances, is that what you mean? If so, that means 2 mosfets (for each polarity of AC). Would be a good replacement for a relay in terms of efficiency, but efficiency isn’t on the priority list here, since its just like 0.5W of power dissipation through the relays coil.

GoForSmoke: What transformer? Switchers use transistors.

I honestly don't know, but I suppose modern switch power supplies do not just put 220V rectified peaks through a transistor in pulses to a buck converter to generate 5VDC. You just need to step the AC down before doing anything to it.

Zengit: Use a mosfet to conduct AC current to home appliances, is that what you mean? If so, that means 2 mosfets (for each polarity of AC). Would be a good replacement for a relay in terms of efficiency, but efficiency isn't on the priority list here, since its just like 0.5W of power dissipation through the relays coil.

That's funny since it started as turn 220AC to 5V and switch that.

Zengit: I honestly don't know, but I suppose modern switch power supplies do not just put 220V rectified peaks through a transistor in pulses to a buck converter to generate 5VDC. You just need to step the AC down before doing anything to it.

Since that's NOT how it's done I leave you to find the transformer in a switching power supply.