LDO linear regulator on a LED driver board

[aiq25]

I have a Meanwell NES-350-36 DC-to-DC converter with 36V nominal output. I'm currently designing a LM3414 LED driver board. I was thinking about adding an LDO linear regulator to get a 5V output so that I can power my Arduino using the same supply and won't need a secondary DC supply. It should work but the huge voltage drop is definitely a concern. I'm thinking of adjusting the output of the Meanwell to be at about 38-39V, so I can have more LED's in series. 38-39V to 5V is a huge drop but I don't think the Arduino and the few other circuitry I will have will need much current, maybe 100mA max. That means maybe like a 3.4W power dissipation around the regulator. I don't know if that's too much power or not for the regulator to dissipate. Maybe I can put two regulators in series and have a two stage drop to get to 5V. Any thoughts/suggestions? The reason I want to use an LDO is so I can incorporate it into the same LED driver board.

Thinking about maybe using a LM2936 or TPS7A6550Q. Maybe even a TPS7A6533Q if I have enough room on the board, I'm sure there will be a need for 3.3V sometime in the future.

Right now I'm just planning everything, I will probably get the board design finished in the summer and have a PCB made by July/August.

 

[oreo57]

Thinking about maybe using a LM2936 or TPS7A6550Q. Maybe even a TPS7A6533Q if I have enough room on the board, I'm sure there will be a need for 3.3V sometime in the future.

LDO info you may need:

Then LDO efficiency is simply (Vo/Vin)*100%. Because the LDO has no way to store significant amounts of unused energy, power not delivered to the load is dissipated as heat within the LDO.

See equation 2 for power dissipation:
http://www.analog.com/library/analogDialogue/archives/43-08/ldo.html

LDOs are most efficient with small differences between supply voltage and load voltage.

not looking promising though..

 

[aiq25]

I think I will have to think about this some more and maybe make a prototype on a breadboard. I really don't care about it being the most efficient but I don't want to ruin the longevity of the part either. Perhaps using a multistage would work better.

In the future i might look into step-down switching buck converters but I was just curious if this would work or not.

 

[O2Surplus]

I think I will have to think about this some more and maybe make a prototype on a breadboard. I really don't care about it being the most efficient but I don't want to ruin the longevity of the part either. Perhaps using a multistage would work better.

In the future i might look into step-down switching buck converters but I was just curious if this would work or not.

Add the provision for mounting a MeanWell SCW05C-12 to your PcB. It's the same size as a MeanWell LDD-H, so it won't take up much room. It's rated for up to 72Vin, so you don't need to worry about blowing it up. I use them to drop 48V down to 12V for cooling fans ect.. and also to supply a UA7805 regulator to power the Atmega328P-AU chip on my A6211 5 channel drivers. They're a little pricey $12 each, but they eliminate a lot of headaches.:dance:
Here's a photo- There's a UA7805 regulator hiding under the SCW05C-12.

 

[aiq25]

That's neat, will look into it. What kind of drivers are those O2Surplus?

 

[O2Surplus]

That's neat, will look into it. What kind of drivers are those O2Surplus?

They're a Buck regulator based on the Allegro MicroSystems A6211.

 

[mcgyvr]

Just add a switcher.. not a linear regulator.

 

[Nenad]

They're a Buck regulator based on the Allegro MicroSystems A6211.

Dear O2,

I am following your work for some time and you have inspired me to build an led driver board with some additional tweaks :rollface:. I am interested in a6211. The only problem is that i live in Serbia and the shipping from DK is quite expensive. I've seen on one of your post that you have obtained a6211 from china. Could you, please, send me the store link.

Thank you,
N

 

[aiq25]

Just add a switcher.. not a linear regulator.

Yea after rethinking this I'm going to go with a switch mode supply. I just wanted to use linear because they are simpler to use. Thanks.

 

[mcgyvr]

Yea after rethinking this I'm going to go with a switch mode supply. I just wanted to use linear because they are simpler to use. Thanks.

simpler till the drawbacks come out

Look at Recom if you want "simple" and "switcher"
Like this
http://www.digikey.com/product-detail/en/R-78C5.0-1.0/945-1395-5-ND/2652148

or just roll your own.. There are plenty of chips out there that just require a few external components..

 

[oreo57]

simpler till the drawbacks come out

Look at Recom if you want "simple" and "switcher"
Like this
http://www.digikey.com/product-detail/en/R-78C5.0-1.0/945-1395-5-ND/2652148

or just roll your own.. There are plenty of chips out there that just require a few external components..

OK I have to ask not being to knowledgeable about these:

Most want an analog and or unregulated input.. How do they behave w/ a regulated or switching PS?

http://www.recom-power.com/pdf/Innoline/R-78Cxx-1.0.pdf

Would you need to smooth the input (some) w/ a R/C circuit?

 

[mcgyvr]

The work just fine being powered from another switcher..
And with any regulator its always a good idea to caps on the input and output for decoupling/transient response,etc...

 

[O2Surplus]

simpler till the drawbacks come out

Look at Recom if you want "simple" and "switcher"
Like this
http://www.digikey.com/product-detail/en/R-78C5.0-1.0/945-1395-5-ND/2652148

or just roll your own.. There are plenty of chips out there that just require a few external components..

That RECOM's only 8 bucks and change. Not a bad deal considering it's all the OP would need. Just remember that it's only rated for 42V. The nearly impossible to find Meanwell SCW05C-5 is rated for 72V, so it works great with 48V DIY led projects.

 

[oreo57]

The work just fine being powered from another switcher..
And with any regulator its always a good idea to caps on the input and output for decoupling/transient response,etc...

Good to know.. thanks

 

[oreo57]

That RECOM's only 8 bucks and change. Not a bad deal considering it's all the OP would need.

The other ones I found (and if I remember correctly, higher input limit) were $15

http://www.st.com/web/en/resource/technical/document/datasheet/CD00000080.pdf
http://www.mouser.com/ProductDetail...kpid=2234230&gclid=CIzMy67I2MMCFUQ8gQodbjsA9g

 

[d0ughb0y]

linear regulator run hot with that big voltage difference.
36-5= 31v. if you need 5v 0.5a, that is 0.5ax31v = 15.5watts heat dissipation.

buck converter is the best solution.
there are buck converters that use LM2596HV that can take 60v input. way cheaper than using meanwell.

 

[perkint]

Those little recoms do look nice - not many places stock them over here and as usual, they work out about the same number of GBP as USD (so they cost the equivalent of about $13 and change) but not too bad...

Tim

 

[mcgyvr]

linear regulator run hot with that big voltage difference.
36-5= 31v. if you need 5v 0.5a, that is 0.5ax31v = 15.5watts heat dissipation.

buck converter is the best solution.
there are buck converters that use LM2596HV that can take 60v input. way cheaper than using meanwell.

Yeah thats why I said "roll your own"..
If you are building your own board its always going to be cheaper to stay away from "modular/all-in-one components"

 

[aiq25]

I'm planning designing my own buck converter using the LM2596HV chip, it looks rather simple to do. I'm thinking maybe I will have a 5V and 12V on the same board. I'll let you guys know how that goes.