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Topic: 48v to 12v dc converter (Read 425 times) previous topic - next topic

Qdeathstar

Sep 10, 2019, 05:13 am Last Edit: Sep 10, 2019, 05:15 am by Qdeathstar
Hello guys,

i am working on a project to control vast amounts of leds. Due to the long distances and current requirements involved, i plan to distribute 48v and step down to 12v locally.

Originally, i was going to use these

https://www.amazon.com/uxcell-Step-Down-Waterproof-Converter-Transformer/dp/B01ENGOA4S

one for each 5m of led strip.  However, i would like to make the project modular... and easier to install so i found some connectors i can make a pcb to distribute power and make the project modular but for this to work i need to be able to put the converter on my own pcb so i can get rid of all the wiring...

I found these:

https://www.mouser.com/ProductDetail/TDK-Lambda/I3A4W008A033V-001-R?qs=sGAEpiMZZMt6Q9lZSPl3RQsOIly2NLEkmTVN%252BtkV7YUVCu8Gyj6vkQ%3D%3D

But i think in the quantity i need for the project, i can make my own for a better price. What is in the converter from uxcell? Is it just a control chip, diode, mosfet, inductor and capacitors? What determines the current output?  I need a minimum of 80w @ 12v....
A creaking creeping shadow
stiff against the freezing fog
glares at a tickless watch.

Time has failed him -- all things shall pass.

Grumpy_Mike

Quote
But i think in the quantity i need for the project, i can make my own for a better price.
Making a buck or boost converter is one of the hardest things to do in electronics. I have managed many specialist power supply engineers in my time and have never had one that could make a successful design in less than three iterations of the design.

The big problem is stability, unless the PCB is "right" they will go unstable at certain currents. This gets more critical as the current increases.

There are cheaper designs on eBay but the ones I have seen and bought claim current capabilities that are totally unrealistic. One could even say a total lie.

Component choice is also critical especially the inductor.

Wawa

Efficiency drops with a larger voltage difference.
48>12 is a 75% drop, and efficiency could drop to ~90%,
meaning 80watt could dissipate about 8watts in the converter.
I doubt a 1" x 3/4" board can handle that with just air cooling.
Leo..

manveen_singh

The big problem is stability, unless the PCB is "right" they will go unstable at certain currents. This gets more critical as the current increases.
were you making the converter with an IC like lm2596 ? or were you using some mosfter f ,inductor or other passives to make your converter ?

Grumpy_Mike

Quote
were you making the converter with an IC like lm2596
Yes of course, and following the manufacturer's recommendations as to PCB layout. And remember these were experienced professional engineers.

Qdeathstar

I was able to successfully design a 12v to 200v dc dc converter,  but was low current...

It seems like inductor choice is the bigger problem... then keep the tracks short and wide... I was actually able to find a detailed data sheet last night.

Just had to know the right search term "switching voltage regulator"...

Sadly I'm on my phone so I can't post the data sheet, but it has a drawing for a 75 watt power supply which I can make work if I had too by lowering the brightness of the leds a little.. they aren't going to be full white on most of the time anyway.
A creaking creeping shadow
stiff against the freezing fog
glares at a tickless watch.

Time has failed him -- all things shall pass.

Qdeathstar

Once one design is working, certainly it has gotten posted somewhere on the internet? I don't need to reinvent the wheel...
A creaking creeping shadow
stiff against the freezing fog
glares at a tickless watch.

Time has failed him -- all things shall pass.

wvmarle

There exist constant current LED drivers that take a wide voltage range as input. Those may be suitable for your project as well.

Where does that 48V come from?
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

MarkT

48V is the highest standard DC voltage without legal safety issues.  Many systems use 12V, 24V, 36V, 48V, 60V, 72V.  At/above 60V its no longer "low voltage" so various safety regulations apply.  Power over Ethernet uses a nominal 48V for instance.

Note that a multiple of 12V is used due to the availability of 12V lead acid batteries.

Mains supplies producing these voltages are fairly commonly available, I assume that's the original power source,
and that there's a reason to not supply mains cables everywhere within the project.  Low voltage wiring can be
much thinner for instance since the insulation doesn't have to be so thick.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

Qdeathstar

I am powering ws2812b leds so I don't think a constant current driver will be suitable. I'm just a little surprised there isn't a board layout that works laying around the internet somewhere. Seems like it would be fairly standard..

I am getting the 48v from a meanwell power supply dropping the power for the reasons MarkT has illustrated
A creaking creeping shadow
stiff against the freezing fog
glares at a tickless watch.

Time has failed him -- all things shall pass.

Qdeathstar

#10
Sep 11, 2019, 04:36 am Last Edit: Sep 11, 2019, 04:37 am by Qdeathstar
datasheet for the chip i'm considering using, it has a nice drawing for 75w...

https://www.analog.com/media/en/technical-documentation/data-sheets/3845fd.pdf
A creaking creeping shadow
stiff against the freezing fog
glares at a tickless watch.

Time has failed him -- all things shall pass.

wvmarle

I am powering ws2812b leds so I don't think a constant current driver will be suitable.
Neither would be a 12V supply... Those things need 5V, and the standard flexible strips a bit more than one power point every 5 meters, you will have to place 5V wires in parallel and connect them every meter or so. If you have the 30 LED/m strips you may get away with powering it from the middle but still not a good idea. With any higher numbers of LEDs, no chance with a single power point per 5m strip.

By the way, remember to connect the GND and DI/DO between the strips, NOT the 5V.

datasheet for the chip i'm considering using, it has a nice drawing for 75w...
You're never going to replicate anything near that with a home-built circuit.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

Qdeathstar

i have got 12v strips :P. Google it brah.

Why can't i replicate it? It's very detailed even down the the component choice. Only they they didn't specifically list is the model inductor but they did give a value, and elsewhere in the datasheet it has some detailed information about picking inductors...
A creaking creeping shadow
stiff against the freezing fog
glares at a tickless watch.

Time has failed him -- all things shall pass.

wvmarle

#13
Sep 11, 2019, 02:37 pm Last Edit: Sep 11, 2019, 02:39 pm by wvmarle
I am powering ws2812b leds
Have you checked the datasheet? It clearly states supply voltage maximum 5.3V.

i have got 12v strips
One of these two is false. WS2812B LEDs can NOT handle 12V.

I'll take your word on the 12V and direct addressable part, but the LEDs are certainly not WS2812B. Maybe your strips are outfitted with WS2815 LEDs. Those are in fact designed for 12V supply, and I've seen quite some places falsely selling them as "12V WS2812B".

Why can't i replicate it? It's very detailed even down the the component choice. Only they they didn't specifically list is the model inductor but they did give a value, and elsewhere in the datasheet it has some detailed information about picking inductors...
Good luck getting the PCB just right for it to work with reasonable efficiency.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

Qdeathstar

#14
Sep 11, 2019, 03:49 pm Last Edit: Sep 11, 2019, 03:54 pm by Qdeathstar
I see you googled it, congrats ;)

The also have/had led strips with dc/dc converters built into the strip bu said can't find them anymore... probably they didn't work too well...
A creaking creeping shadow
stiff against the freezing fog
glares at a tickless watch.

Time has failed him -- all things shall pass.

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