alternative to transformers for ac to dc conversion

so i am currently trying to come up with solutions to replace using a transformer in an ac to dc power supply. this might be my ignorance but the only high current transformers i have found are expensive and larger. are there alternatives to using a transformer?

my current thoughts are to use a rectifier on ac input then to a capacitor large enough to stay charged under a large load. this is the part im not sure off but then use a n channel mosfet to take the 78v to 12v using a duty cycle of like 16% then another smoothing cap. Is this a solution? are there better transformerless solutions? am i missing all the cheap small hi capacity transformers(about 10 Amps)?

Thanks in advance.

I am missing several pieces of the puzzle here.

Modern switchmode supplies have replaced most of the transformer based supplies.
You can buy a 12volt/10A for peanuts on ebay.
Look at a laptop supply. 19volt/5A.
20 years ago you needed a supply the size of a shoebox for that.

What do you need...
Leo..

its not as simple as it sounds to make a switching power supply. You have to wonder how they make them as cheap as they do. If I was after a 10amp I would be looking at a xbox power supply.

yeah i was looking up SMPS's and they dont seam simple. im looking for something simple that i can fit on a protoboard. it doesnt have to be really clean just has to work.

Easy. Buy an AC to DC supply board on Ebay, solder pin header onto the output, and stick it onto your protoboard :wink: - they're cheap there.

You can make a buck/boost converter at home (that's DC-DC converter), and it's not that bad. I've done it on my protoboard with SMD part outlines on it, and it worked well enough. You can also buy modules on ebay for less than you could get the parts for.

The problem with that is that very few of those converters would take such a high input voltage. The AC-DC converters typically have a little transformer in them, and use clever tricks to be able to make it smaller. So yeah, I'd just buy a pre-made module. Working with such a high voltage can be a little dicey anyway.

Also, check out the protoboards in my tindie store, I've got a few styles similar to what's visible in my avatar, and if you like building on protoboard (like I do) you might like it.

You did not say what output voltage and current you need.
Is this for your 12volt fans from a previous post?
Leo..

What you describe in your original post is both illegal and dangerous. Also running mains into a prototype board is not a good idea, it could kill you.

Switch mode power supplies are difficult to make and require a proper printed circuit layout to make them stable. You are better off buying a sealed unit.

Wawa:
You did not say what output voltage and current you need.
Is this for your 12volt fans from a previous post?
Leo..

no i have a lipo charger that needs 100 watts or more. i could buy something small but i wouldnt learn anything then.

gpop1:
its not as simple as it sounds to make a switching power supply. You have to wonder how they make them as cheap as they do. If I was after a 10amp I would be looking at a xbox power supply.

They can make them cheap because, while they are rated at some voltage and some current, they cannot do both at the same time. I bought a Chinese 12 volt 10 amp switching PSU off Ebay. It does supply 12 volts. It will supply 10 amp, but at 5 amps, the voltage has dropped to about 8 volts.

So beware of actual capacity, not advertized maximums!

Paul

cbrunnem:
no i have a lipo charger that needs 100 watts or more. i could buy something small but i wouldnt learn anything then.

100w is less than 1 amp. I thought you said 10amps

Wawa:
You did not say what output voltage and current you need.

Still not answered.

100watt could be 25volt/4Amp
or 12.5volt/8Amp
or 1volt/100Amp

Wawa:
Still not answered.

100watt could be 25volt/4Amp
or 12.5volt/8Amp
or 1volt/100Amp

yep except he said 78v to 12v in the first post.

Worth mentioning that switch mode power supplies have a transformer in them.
Its just that its a ferrite transformer rather than an iron core transformer.
The design and characteristics of the ferrite transformer are extremely important and if you dont get it right
then lots of blown up switching fets or transistors will result.
Designing hi power switch mode power supplies is not a beginner project.

The gimmick they use, is converting to high frequency. If you use high frequency instead of 50/60 Hz, then the transformer can be made very tiny.

Wawa:
Still not answered.

100watt could be 25volt/4Amp
or 12.5volt/8Amp
or 1volt/100Amp

It's in the original post.

gpop1:
100w is less than 1 amp. I thought you said 10amps

100w at 12v my lipo charger isnt Ac

Hi,
Can you post a picture of your Lipo charger please, and its specs.
It seems confusing as to the voltage and current it needs and what it is charging? (Battery specs.)

Tom… :slight_smile:

TomGeorge:
Can you post a picture of your Lipo charger please, and its specs.
It seems confusing as to the voltage and current it needs and what it is charging? (Battery specs.)

My! What rudeness!

Asking a poster to provide full details. :roll_eyes:

That would be like shooting a caged lion - it's just not sport!

Sorry…I’ll go to the naughty corner… :slightly_frowning_face:

I was unaware that lipo chargers weren't as common as I thought.

That's it. I rounded up the wattage and amps as I dont know it's efficiency. I know 12v and 10 amps don't match obviously with 100 watts but I didn't realize people would pick at small details.

I think you haven't got a firm grasp on Ohm's law yet.

According to the datasheet, this charger requires an input of ~10-18volt.
It might draw upto 7Amps from a 12volt supply (12x7=84watt).

So a 12volt/10A supply is a perfect match for this charger.
Leo..