Hi,

I'd be interested to replace the batteries in one of my projects with a power supply. Specifically, I'd like to directly integrate a power supply that works with a 110V-240V input range (roughly) and outputs around 3.6V (though I'm somewhat flexible there). At 3.6V I should never need more than 400mA, but to be safe it would probably be better to support a little more.

I'm looking at this as somewhat of an educational exercise for myself, so I don't want to simply hook it up to a bought adapter or similar. Furthermore, because of what I'm trying to do it should be:
- small (I'd like to get this into a cube of about 2x2x2cm, along with some other components, if that's even possible)
- cheap (if components were acquired via wholesale $3 or less)
- energy-efficient (har har har just to add one more)

As you can probably tell I have no clue of power electronics, which is one of the reasons why I'd like to do this exercise. I'm assuming what I'm asking for here is at least pushing it, if it's possible at all, but I currently don't even have a good understanding of what types of power supplies and techniques I should be looking at. I started searching around, but got lost in the massive amount of options and variants with different caveats, so I was wondering if given these goals, what options / components / brands / howtos / books / descriptions / ?? would you recommend me looking at?

Any advice or suggestions are highly welcomed

Thanks,
Thomas

 

Given your admitted knowledge base and price range no its not possible.

Spend $3 - $5 and buy a 5 volt USB adapter and put two diodes in series on its 5 volt output to get a ~1.2 - 1.4 volt forward drop and you will have a universal input 85 - 250 VAC to 3.6 - 3.8 VDC adapter that both compact and safe to use.

 

Buy yourself a switchmode psu, like a phone charger plenty in junk shops or ebay.

 

Check out Power Integrations' Linkswitch family. Read the application notes to get an idea difficulty of making a safe offlline switcher. Personally, I prefer to buy ready-made power supplies and let some manufacturer worry about safety and reliability while I concentrate on the interesting part of the project.

Check it out:
https://ac-dc.power.com/products/linkswitch-family/

 

Hi,

I'd be interested to replace the batteries in one of my projects with a power supply. Specifically, I'd like to directly integrate a power supply that works with a 110V-240V input range (roughly) and outputs around 3.6V (though I'm somewhat flexible there). At 3.6V I should never need more than 400mA, but to be safe it would probably be better to support a little more.

I'm looking at this as somewhat of an educational exercise for myself, so I don't want to simply hook it up to a bought adapter or similar. Furthermore, because of what I'm trying to do it should be:
- small (I'd like to get this into a cube of about 2x2x2cm, along with some other components, if that's even possible)
- cheap (if components were acquired via wholesale $3 or less)
- energy-efficient (har har har just to add one more)

As you can probably tell I have no clue of power electronics, which is one of the reasons why I'd like to do this exercise. I'm assuming what I'm asking for here is at least pushing it, if it's possible at all, but I currently don't even have a good understanding of what types of power supplies and techniques I should be looking at. I started searching around, but got lost in the massive amount of options and variants with different caveats, so I was wondering if given these goals, what options / components / brands / howtos / books / descriptions / ?? would you recommend me looking at?

Any advice or suggestions are highly welcomed

Thanks,
Thomas

An advanced project would be cracking open a USB wall wart and changing the voltage sense resistors - but the safety implications aren't trivial.

The best approach would be a LDO 3.3V 3-terminal regulator supplied by a stock USB wall wart. A forward biased silicon diode in the GND pin would probably raise the output too much, a Shottky barrier diode probably not enough. Some commercial products lift the GND pin a little bit with a voltage divider across the output.

If its a low current application; you can use a USB wart with a resistor and shunt regulator. The TL431 can absorb 100mA as long as the set voltage doesn't exceed the dissipation limit. There are ways to boost the current handling - but they eat into the voltage headroom. Currently I use a boosted 431 in a USB wart powered lithium charger to 4.2V, so what you want should be do able.

 

Thank you all for your responses, very much appreciated.

I do agree that in general I shouldn't spend too much time on building my own power supplies and rather buy one for home projects (as a few of you suggested and I've done in the past). However, for my current project I also want to validate that what I have in my mind regarding size & cost would actually be doable in practice, given enough help from more experienced engineers.

Based on this thread so far I was already able to confirm that I should indeed look into these offline switchers, which I thought was the case but wasn't sure if there are other / better alternatives out there. In particular the referenced Linkswitch family seems exciting and somewhat approachable for me, thanks!

Are there any other product families you'd recommend for me to look at (e.g. ones that integrate even more of the necessary circuitry for this type of power conversion into a single component)? Note that the 3.6V from my original post was just meant as a point of reference, based on my current requirements, really anything between 3-5V should be fine.

If you have any other suggestions for what I could look at or read (e.g. good knowledge source for this sort of thing, etc.) please let me know.

Thanks,
Tom

 

You cannot hit your size and cost targets without building 10,000 pieces per ***day***. That's what it took for Apple to hit your targets, but only because the stuff is designed and built in countries with "relatively few" labor and environmental laws. In the US, no way, ever.

The transformer alone took a team of designers six months to perfect. To be fair, they had to meet EMI regulations for every country on the planet.

ak

 

I could easily but these kinds are not permitted here.

with a LNK IC you only need a few parts and many can be omitted under certain circumstances.
For instance the little EMI from 0.3 Watts normally doesnt bother anyone. If you have ceramic tiles in the room you dont need to bother fusible resistors. If you have surge arrestors in the house already you dont need to bother about failure from a sudden surge.

I can build with parts not even costing 50 cents (without enclosure fuse etc).

Whatshowever, if you sell customer, you dont know their setup environment and must deal with worst possible case i.E. highly flammable tissues some nutcase wrapping the supply into such tissue and lives old wooden house you get a surge the thing bursts into flames there you go...

i.g. the lower the cost the more likely the thing will fail some day i absolutely love these lithium power banks the USB connector for charging breaking off the PCB after 2 weeks and the booster burning out when plugging in something drawing more current than permitted, no polyfuse not short circuit proof.

So if you dont understand possible hazard chains of incidents worst possible case scenario dont ever tinker with this technology and buy the best available quality ready made modules from professional distributors. And btw. a wooden house without smoke detectors and fire extinguisher and exit routes statistically is a death trap. The older it gets, the worse.

 

Thank you both for your responses - a good portion of realism is always a good thing too
I might have not expressed myself well enough before: I'm not interested in building this myself and making heavy use of it throughout my house. Rather, I'm considering this my personal viability-study and at the same time trying to educate myself, potentially building a prototype I'd merely use in a controlled environment, while still using a bought power supply for validating the rest of the project. Hope this makes sense.

In any case, all advice and suggestions so far have been very appreciated, if you have more, I'd be very interested

Thanks,
Tom

 

National, Linear Tech, and Power Integrations all have arrangements with transformer companies. For a "standard" design using some of their parts, you can buy the switching power transformer off the shelf rather than developing one from scratch.

ak

 

National, Linear Tech, and Power Integrations all have arrangements with transformer companies. For a "standard" design using some of their parts, you can buy the switching power transformer off the shelf rather than developing one from scratch.

ak

Some of those companies also sometimes include winding details on their appnotes.