suspicious buck converter on ebay

[autotel]

(TLDR at the end)

I have read that buck converters waste less power than linear regulators. I am doing a project that has a 3.3 volts microcontroller, but it needs to be fed from a 12 volts power supply. This means that if I were to use a linear converter, it would loose a lot of energy heating up. I tried it, and indeed, the regulator works as an electric stove. I decided to try a buck converter, and went to ebay. Bought this so-called TB-42229 board.

It hasn't arrived, but to earn time I started drawing a schematic that would use the same components, but came to learn that this board is using an https://www.ebay.com/itm/322574255177. In the datasheet there is nothing that would lead me to think that this is a buck converter. Looking online, nothing indicates this either. However, I haven't found anything that states that this is not a buck converter either.

So, is this a small scam? Did I just wasted some money on yet another electric stove?    I have seen many fake buck converters on ebay, but they all have a negative comment indicating this.

link: https://www.ebay.com/itm/322574255177

TLDR: bought buck converter, but it's based on an LM317. I know little about this chip, but doesn't seem to be one. Have I just bought a linear regulator?

[OwO]

It's not a buck converter. There is no inductor on that board. I bet the seller just copy and pasted the title from some other listing.

[Cyberdragon]

 

It DOES say "linear regulator". Granted they shouldn't say "buck converter" as well but that is ebay tag spam for you. It should have also been painfully obvious just looking at the board that there's no actual converter coil.

[Ian.M]

@Autotel,
How much current do you need at 3.3V?   (both abs. max. and normal running please)
Do you need a low power standby mode?

There's nothing particularly scary about buck converter designs - if you stick to choosing an IC from a major manufacturer with good design support, copy the recommended PCB layout around the chip, (PCB art for their own eval board is a big help here) and use an inductor with a high enough saturation current and low enough losses to meet the design requirements.   

OTOH for a one-off, that doesn't need over half an amp, a 'chinesium' 50KHz fake LM2596 EBAY buck module may be good enough.  Add a *GOOD* crowbar circuit if the parts on your 3.3V rail are high value!

[autotel]

yes, I was way too naive. I could anyways find some excellent buck converter boards. they have surprised me a great deal on how forgiving they are. For instance, I supplied them 12v ac by accident, abd they still produced a great steady output. I also noticed that when I move the stepper motors manually (which are fed by the same supply as the converter), it gives voltage aswell. Fun stuff.
I think I bought this one (https://www.partco.fi/fi/teholaehteet/dcdc-jaennitemuuntimet/19066-mp2307-cv.html?search_query=step+down&results=44) and a similar one in slightly bigger form factor.

thanks for the notes, @Ian.M