Hello, Looking to build a step down using xl6009

[docprototype]

Hello guys, I have bought several buck boost converters as i got them pretty cheap. Now i need 1 of them to step down the voltage.


I want to knwo if somebody can help me understand more of this step up converter and if i can convert it to step down the voltage as well.
I saw some videos and sellers using step up/down converters with xl6009.

Thank you in advance

[Vovk_Z]

And what datasheet say about this?
It seems to me there are so many those cheap modules on eBay (and not only) so it is much easier to buy a ready-made one.

[sleemanj]

As a boost converter it uses a single inductor, in buck-boost converter mode it uses a coupled inductor and an extra capacitor.

It would not be practical to hack your existing boost module into a buck module, the result would be poor, and certainly more expensive to do so than just buy a buck module off ebay aliexpress or whatever local sellers you might have for like $3 or whatever.

[docprototype]

Mostly it was for the sake of learning more about them in a practical way. Thank you both for the replies.

[Rick Law]

Mostly it was for the sake of learning more about them in a practical way. Thank you both for the replies.

These modules are getting so cheap that the parts you need to make a conversion will cost many times that of a new module.  But since is for learning, it has some value.

First, you start with the datasheet for the heart of the main thing.  The rest of the PCB is designed to support "the main thing" - in this case the brain is xl6009, so off to search for the datasheet for this brain.

I found one here:
https://www.nikom.biz/pdf/XL6009.pdf

Read it carefully, you will see that on page 1 "General Description", it is quite clear (in line 2)  that this guy's brain does "step up" (aka boost).  So, if you want to step-down (aka buck), it is out of this guy's capability.  This guy will need a brain transplant.

While you are looking at the xl6009's datasheet, page down a bit to page 3, there is the "typical application" circuit right there.  This gives you the idea of how the xl6009 should be connected.  This circuit is typically the minimalist circuit - nothing fancy, just bare minimum to make it work.

For the module you have at hand: If you trace your PCB and map out your module's circuit diagram, chances are, it will be very much like that minimalist "typical application" circuit.  It will be educational to do that tracing and to understand where your module's circuit differ from the "typical application" circuit in the datasheet.

Second, knowing that the current brain in the skull  (xl6009) is not going to do it, now you know you'll need a brain transplant for this guy.  To do that, you need to understand how the other brain (in this case, a buck converter) works.  Now there are chips that can do both, let put that aside for the time being and stay with a buck-only.  I've used the XL4015 buck converter from the same manufacturer, so I will use this as candidate for this part of the discussion.

Now you seek and hunt down the datasheet for the xl4015 buck.

I found one here:
http://www.xlsemi.com/datasheet/XL4015%20datasheet.pdf

Again, on page 3, you see a "typical application" circuit diagram.  Print it out as well.

Third, now time to look at both xl6009 and the xl4015's circuit diagram side-by-side.  Now you see how much work and if it is feasible at all.  Don't forget, besides pin-outs (can you cut and patch to switch say for example V+ on pin 3 verses say V+ on pin 1 on the other chip).  Also, the datasheet may point out certain part(s) needs to be close to the chip.  Is there room to do that on this PCB?

Forth, hunt for other candidates.  I think XL6019 does both boost and buck.  There are of course other candidates.  If you do want to convert your PCB.  Now you have to map out where you CUT, where you ADD.  You can find the best candidate fitting your criteria/priority.  Whatever motivates you.

Fifth, a final suggestion.  Do you have any old car cell-phone charger?  Older ones that you no longer use...  I have a dozen or so of them, mc34063 (or variant) was quite typical.  That chip is rather forgiving.  In my own learning process, I converted a number of them by just trace cutting, rerouting, patching, and just a few passive (cheap) components.  Since they are for old cell phones no longer in service, they are free.  Personally, I learn quite a bit from those experiences.  Also, in getting it done, I had to learn how to measure inductance of inductors originally on the board.  Side lessons of this nature are also of value.  I've forgotten most of the details of how I did it.  But having done (and understood) those little side lessons were very educational.

Good luck with your pursuit...

[james_s]

It looks like Rick covered everything pretty well.

Something to keep in mind if it hasn't been mentioned here already is that many/most of these crazy cheap regulator modules use counterfeit parts. I have a bunch of the step-down ones based on the LM2576 or whatever that is and while they work fine they are NOT actually LM2576 parts, they don't run at anywhere near the same frequency that the genuine part does. If you're trying to modify an existing module this could make a big difference, the part you have may not support all configurations shown on the datasheet for the real deal.

[docprototype]

@rick law

Thank you alot mate for taking the time and writing that. Very helpful so ill try give it a shot. Trying to learn aswell

@james yeah just came across a video pointing out the counterfeits modules. Will check more of that