# Constant Current Power needed... I'm confused...



## tedoro (May 15, 2020)

Hi, I have an art project and I have found a hundred bulbs (9-12v 3 watt COB) and I desire to not burn my house down.

https://www.ebay.com/vod/FetchOrder...sId=957416770021&_trksid=p2057872.m2749.l2673

I vaguely understand that these bulbs can continue to pull more current as they heat up, causing problems... so a power supply that caps their consumption is safer than one that would not. I found this...

https://www.amazon.com/dp/B07DWM42M5/?tag=cpf0b6-20

So I would wire up 320 watts worth of bulbs and I should be good?

t


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## DoctorMemory (May 16, 2020)

Well, the 3W LEDS are rated for 260-280 mA and to drop 9-12V. You will have to series the LEDs and run 260-280 mA thru the whole string. You cannot parallel the LEDs unless you want major headaches.

The supply offers 700 mA which is too much, you want 260-280. They want you to buy a MSSL200 to set the current lower.

The supply will put out 183-457 VDC depending on the AC voltage fed into it. You will need 12V for each LED; if you feed it with 120VAC it will put out around 244VDC which would allow around 20 LEDs in series. If you want more you'll need another power supply for each new string. That supply is overkill with 700 mA output, you should look for something in the 280-290 mA range. Then see how many LEDs at 12V each can be strung, and then how many power supplies you will need, one for each string.


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## tedoro (May 16, 2020)

I am very appreciative that you took the time to respond, especially to a noob like me (I just signed up). I am an artist here in Portland Oregon and often use LED's but honestly, you can do a ton without knowing much, which is me in a nutshell.

I've been testing with these in parallel. I will stop that.

I have 12 strands of eight bulbs, which can easily be 6 strands of 16 bulbs. So let's go with the latter.

First off, is constant current the correct way to handle this... its just what I read somewhere. I am completely willing to take your advice whole heartedly.

I am concerned with heat, and would like to be able to reduce the wattage to reach the sweet spot of good light output and low heat.

So, 16 bulbs would want 192 VDC at 260-280 mA if I am following you. Shoud that be a constant current supply? Do they make them with a voltage adjustment such that you needn't buy a second device?

Again, your help is very appreciated. I will owe you big.


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## tedoro (May 17, 2020)

I suppose it would be better for me to shoot for the desired brightness from the design, and forego the adjustability. My testing of these bulbs have shown that when run at 2.5 watts they are bright enough and not hot to the touch. So what power supply would be right for 16 (or eight) strung in parallel?

t


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## tedoro (May 17, 2020)

This seems to be as close as I can find... (I barely know what I am doing...)

https://www.amazon.com/dp/B071CJ6M4Q/?tag=cpf0b6-20

for a eight lights strung in series. But its 300ma and likely running it at less than 2.5 watts.

or this is close too...

https://www.amazon.com/dp/B00ZCB2JSS/?tag=cpf0b6-20


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## JustAnOldFashionedLEDGuy (May 17, 2020)

Ignore DoctorMemory. He is giving you advice on something he does not understand. The driver you linked will put out 700mA. It will do that if you keep the string voltage in the output voltage range.

If you connect 20, 12V LEDs in series it will output 700ma and the voltage will be around 240v, but probably higher as your LEDs are not rated for that current. The input AC voltage has nothing to do with the output voltage.


You could parallel LEDs with likely not too much issue. Modern LEDs are manufactured to better tolerance. It's not ideal, but usually no issues and many many led products do this. The safer way is normally put parallel 3 together so you get a 700ma rating and the stack those. I would go 4 in parallel, and then stack them to average 175ma per led but some will be higher and some lower. Make sure they are close thermally. Voltage varies with temp. You can put 20 in series and then 4 of those strings in parallel but greater chance of mismatch.


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## JustAnOldFashionedLEDGuy (May 17, 2020)

And caution, those DC voltages are high and DC is more dangerous than AC. Treat it with respect.


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## tedoro (May 18, 2020)

JustAnOldFashionedLEDGuy said:


> Ignore DoctorMemory. He is giving you advice on something he does not understand. The driver you linked will put out 700mA. It will do that if you keep the string voltage in the output voltage range.
> 
> If you connect 20, 12V LEDs in series it will output 700ma and the voltage will be around 240v, but probably higher as your LEDs are not rated for that current. The input AC voltage has nothing to do with the output voltage.
> 
> ...



Okay. I'm still a bit overwhelmed. Heres the deal. I want to run these 3 watts lights a tad bit less than rated to keep them cool. Numerous strands are needed of 8 bulbs (or 16). I want them very safe. how do I do that? I am finding a bunch of 300ms constant current drivers. Is that too much? (I'm in the US 110v AC) was he right that parallel is not the way to go?

I am using these COB 3 watt led's, but have not chosen the power supply. The world is my oyster... Whats easiest?


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## tedoro (May 18, 2020)

Now I'm mostly talking to myself...

What if I used this power supply

https://www.amazon.com/dp/B07MSBK9GV/?tag=cpf0b6-20

and wired up 8 lights in parallel and put the whole thing on a LED dimmer?

Seems expensive, $30 times 12... and the cost of a dimmer that size. But I gotta get this done.


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## JustAnOldFashionedLEDGuy (May 18, 2020)

tedoro said:


> Okay. I'm still a bit overwhelmed. Heres the deal. I want to run these 3 watts lights a tad bit less than rated to keep them cool. Numerous strands are needed of 8 bulbs (or 16). I want them very safe. how do I do that? I am finding a bunch of 300ms constant current drivers. Is that too much? (I'm in the US 110v AC) was he right that parallel is not the way to go?
> 
> I am using these COB 3 watt led's, but have not chosen the power supply. The world is my oyster... Whats easiest?





Can you send a link to the LEDs that is not to your order, but their product page or similar?

You want to run 100 of them, or do you want to run less? How to you plan to mount them, i.e. how safe do you need the voltage to be? Generally under 60V is somewhat safe indoors, 30V outdoors where wet is an issue. If you are going over those voltages, then you need to make sure people can't touch them, and that you don't have accidental shorts to metal that someone can touch.

Let's say you are going to go 48V, so that appears to be 4 in series. Let's say you do 0.2A per unit. That would be 25 parallel strings, or you could do 25 in parallel, and then stack those 4 high. You would need a 5A output driver.

For high voltage, let's take your 700mA driver and divide it by 4 = 175mA per string. You have 100 LEDs, divide that by 4 = 25 stacked in series with a voltage around 25 * 12 = 300V, but realistically between 250 and 300V. Best to wire those as sets of 4 in parallel and then stack those sets 25 in series. If you do find 1 out of 4 is noticeably brighter than the other, then you can swap that out for another one. Unfortunately it does not sounds like you have the tools to sort them. You could stack them 25 in series * 1, and have 4 strings. Than add a 50 ohm, 5W resistor in series with each string. That will help balance the strings for voltage differences between the strings.


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## tedoro (May 18, 2020)

https://www.ebay.com/itm/311651957952

my apologies

Indoors. 

The mounting is all figured out with heat sinks.

100 led's total.... in strands of 8 led's.

I found this driver that looks like an interesting option to run two of my rows with....

https://www.amazon.com/gp/product/B07R7QQ286/?tag=cpf0b6-20


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## tedoro (May 18, 2020)

feel no need to utilize the power supply I linked... as I haven't purchased it.


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## tedoro (May 18, 2020)

I feel like I would like to have it be a bit smaller, like perhaps having a few power supplies run sections. If I can pull it off without resisters that would be great. 

I really appreciate your write up. for the most part, I can follow it.

Tell me, if I used the 20-24Vdc power supply linked below, could I run eight in series, then parallel two series? When will a series strand start to be too long?

https://www.amazon.com/gp/product/B07R7QQ286/?tag=cpf0b6-20


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## JustAnOldFashionedLEDGuy (May 18, 2020)

tedoro said:


> Tell me, if I used the 20-24Vdc power supply linked below, could I run eight in series, then parallel two series? When will a series strand start to be too long?
> 
> https://www.amazon.com/gp/product/B07R7QQ286/?tag=cpf0b6-20




Your LEDs are ~9-12V, so with a 24V maximum supply, you can only do 2 in series 2*9-12 = 18-24V. Then 7-8 in parallel = 1500/7-8 = ~200mA each. It will probably work, but I am concerned with any driver that has a narrow operating range like 20-24V. That tells me the design could have some issues. 

I would go with something like this:

https://www.digikey.com/product-detail/en/mean-well-usa-inc/LPC-100-1750/1866-3133-ND/7704802

1.75A gives you say 8-10 parallel strings, and 4-5 in series. 4-5 drivers will power everything, but expect some of your 100 units to be "spares". This is <60V, and <100W which is better for safety, but you still need to protect from touch.

If you want to stick below 30V, then maybe this:

https://www.digikey.com/product-detail/en/tridonic-inc/28002153/2538-28002153-ND/12141492


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## tedoro (May 18, 2020)

okay, let me look this over


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## DIWdiver (May 18, 2020)

A string of 8 of those LEDs near full power is going to be 70-90V. This is above the maximum safe voltage, which depending on who you ask is anywhere from 48-60V. If you really need to do that, you have to take extra precautions to ensure that nothing in your system can short to metal that anyone can touch.

I would much rather you wire that electrically that as two strings of 4 in parallel (which could still be physically arranged as one string). 12 strings of 8 would become 24 strings of 4. To run them near full power, but not quite, let's say 250 mA per string. That adds up to 6A.

So to do it that way would require a supply capable of 48V, 6A, with adjustable current limit.

Other ways to keep the voltage safe is 32 strings of 3 (which maybe doesn't fit your design), for which you'd need 36V, 8A; 48 strings of 2, which requires 24V, 12A.

Personally I think the 48V, 6A is a good compromise that keeps both the voltage and current reasonable.

EDIT: Crossed in the mail. I realize this is a bit late to the party!


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## DIWdiver (May 18, 2020)

Yeah, I'd also be leery of a no-name device that costs 1/3 of what a name-brand one does. If it doesn't need to last, maybe take a chance, but if failure is not an option, go with the name brand.


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## tedoro (May 18, 2020)

So if I run 3 in parallel and get 36vdc, then run a bunch of those in series, perhaps 5 times, I would get 1.4 amps... is that your thinking? (my apologies if my nomenclature is improper. 

I was kinda hoping for the cleanest strand of 8 leds I can do... (this is an art project using these as grow lights for plants on a grid)


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## tedoro (May 18, 2020)

DIWdiver said:


> A string of 8 of those LEDs near full power is going to be 70-90V. This is above the maximum safe voltage, which depending on who you ask is anywhere from 48-60V. If you really need to do that, you have to take extra precautions to ensure that nothing in your system can short to metal that anyone can touch.
> 
> I would much rather you wire that electrically that as two strings of 4 in parallel (which could still be physically arranged as one string). 12 strings of 8 would become 24 strings of 4. To run them near full power, but not quite, let's say 250 mA per string. That adds up to 6A.
> 
> So to do it that way would require a supply capable of 48V, 6A, with adjustable current limit.





DIWdiver said:


> Other ways to keep the voltage safe is 32 strings of 3 (which maybe doesn't fit your design), for which you'd need 36V, 8A; 48 strings of 2, which requires 24V, 12A.
> 
> Personally I think the 48V, 6A is a good compromise that keeps both the voltage and current reasonable.
> 
> EDIT: Crossed in the mail. I realize this is a bit late to the party!



Okay, let me think about what you said now.


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## tedoro (May 18, 2020)

_I would much rather you wire that electrically that as two strings of 4 in parallel (which could still be physically arranged as one string). 12 strings of 8 would become 24 strings of 4. To run them near full power, but not quite, let's say 250 mA per string. That adds up to 6A._

_So to do it that way would require a supply capable of 48V, 6A, with adjustable current limit._​
I understand this, or I think I do. Let me put it into my words, to make sure I really do.

I put all the LED's into parallel strands of 4 (48vdc, 250ma). I group two of those strands into series, making my 8 LED strand my design requires (48vdc, 500ma), then put all of those groups in series.... 12 times (48VDC 6000ma)

Is that correct? This seems great!


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## tedoro (May 18, 2020)

What would I search for when seeking the unit?

this looks close:

https://www.amazon.com/dp/B005T6K78K/?tag=cpf0b6-20


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## tedoro (May 18, 2020)

I think I found one!!! A little spendy, but it looks right.

https://www.amazon.com/dp/B06XFJB28D/?tag=cpf0b6-20



MEAN WELL HLG-320H-48A constant voltage and constant current LED power supply
Full range AC input: 90~305Vac
Operating case temperature: -40~+90°C
UL8750 type HL LED power supply
Meet 4kV surge immunity level (IEC61000-4-5)
Built-in active PFC
IP65 durable aluminium enclosure
High efficiency
Output voltage and constant current level can be adjusted through internal potentiometers
Protections: short circuit / over current / over voltage / over temperature
Applications: LED electric display, lighting, LED street lighting and indoor/outdoor lighting
MEAN WELL 7 year warranty


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## JustAnOldFashionedLEDGuy (May 18, 2020)

tedoro said:


> So if I run 3 in parallel and get 36vdc, then run a bunch of those in series, perhaps 5 times, I would get 1.4 amps... is that your thinking? (my apologies if my nomenclature is improper.
> 
> I was kinda hoping for the cleanest strand of 8 leds I can do... (this is an art project using these as grow lights for plants on a grid)




You are getting series and parallel mixed up. Parallel is side by side. Parallel increases current rating. Series is stacked on top of each other. Series increases the voltage.


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## JustAnOldFashionedLEDGuy (May 18, 2020)

You would have 25 in parallel, and 4 in series .... or 25 parallel strings of 4 in series. The former, putting 25 in parallel at a time, then stacking those 4 high in series, is safer. That gives you 270mA for each LED, but with mismatching from paralleling what are cheap LEDs, is probably a bit much for those. It has a pot though that allows you to adjust it down to 3.35A, so you can tune the output. It also has dimming wires that you can hook a 0-10V dimmer up to and reduce it to a much lower current if needed.


I suggest buying it from a reputable distributor, such as Mouser or Digikey. It's a bit cheaper as well: https://www.mouser.com/ProductDetai...OaCslb6T0uJ%2B4qvaR/SmMi35/eVjOw7rr%2Bpz25A==


You may pay more for shipping, but worth it.


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## tedoro (May 19, 2020)

*I would much rather you wire that electrically that as two strings of 4 in parallel (which could still be physically arranged as one string). 12 strings of 8 would become 24 strings of 4. To run them near full power, but not quite, let's say 250 mA per string. That adds up to 6A.
*

Okay, whoops, I know better.... let me try again.

okay, I take all 100 LED's and put them in strands of 4 in parallel (12vdc 1000ma) I take two of those strands and put them in series to make my 8 LED strand I need for the design (24vdc 1000ma) then I take these 12 strings and group two together in series (48vdc 1000ma) and then lastly, take those 6 groups and wire the whole thing together (48vdc 6000ma)

Is that what you were thinking?


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## tedoro (May 20, 2020)

Okay, if I have it right, and this is an okay and safe design that I can run these bulbs a bit lower than rated... what is the procedure on fabricating and testing it? I fear doing one wrong move and blow everything up in a nanosecond. its a fair bit of labor in soldering alone...


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## DIWdiver (May 20, 2020)

Yes, it looks like you have it.


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## DIWdiver (May 20, 2020)

That Mean Well power supply looks perfect. It's a solid brand, and I agree, buy it from a distributor like Mouser, DigiKey, or others. I plugged it into Octopart, and it looks like Newark has the best price at $72.32. Check their shipping, though, as it could swallow most of that savings.

The first powerup is always scary. I'm coming up with no simple way to do it in stages.


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## JustAnOldFashionedLEDGuy (May 20, 2020)

Spend the extra and get the https://www.mouser.com/ProductDetail/MEAN-WELL/HLG-320H-48B?qs=DNaZHaGatO3I17c08YAcZw== ... this is the B model. It has 0-10V dimming wires. Unfortunately the data sheet does not show what happens when the dimming wires are 0V (i.e. you short the two dimming wires together), but normally they would go to the lowest level or 10%. What is not clear is whether that is 10% of the current set with the potentiometer but it should be. That would give you with the dimming leads shorted, 10% of 3.35A or 335mA. That is going to do a lot less damage than 3.35 or 6.7A. You will need 2-3 units in series to get up to 24V before the driver will work properly. But even two in parallel should not be damaged with 335mA.


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## Dave_H (May 21, 2020)

Parallelling LEDs needs some consideration. You could try it and hope you get lucky. With small number of parallel
strings, if one fails open (due to LEDs or merely a bad connection), all current is forced through remaining
string(s) which could cause damage, or a least run brighter and hotter. With large number of strings the effect might be less dramatic,
but brightness could vary across strings.

Inside a LED ceiling fixture I found 24v CC driver with series connection of 8 sets of 4 paralleled SMT LEDs, with no sign
of resistors or any obvious load balancing. They can get away with this by close match of forward voltage
of LEDS (vf binning) and that they operate at approximately the same temperature. Not sure if either is happening
with design in this thread.

With smaller SMT white LEDs I found vf range typically 2.7v to 3.2v at same current and temperature; typically divided into
4-5 ranges ("bins"). Not sure what LEDs being used here have, looking at spec. now.

LEDs have negative voltage coefficient with temperature, which in some cases can lead to thermal runaway.

Osram has (or had) a bunch of good application notes including this...I might be able to dig up a copy; or someone
could search this out.

Not trying to discourage DIY; but the current, voltage and power levels are high and needs caution, especially
if new to the game.

Dave

Interesting article (though a bit older) dealing with 2 parallel case:

https://www.ledsmagazine.com/leds-s...ay-when-driving-multiple-led-strings-magazine


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## DIWdiver (May 21, 2020)

JustAnOldFashionedLEDGuy said:


> Spend the extra and get the https://www.mouser.com/ProductDetail/MEAN-WELL/HLG-320H-48B?qs=DNaZHaGatO3I17c08YAcZw== ... this is the B model. It has 0-10V dimming wires. Unfortunately the data sheet does not show what happens when the dimming wires are 0V (i.e. you short the two dimming wires together), but normally they would go to the lowest level or 10%. What is not clear is whether that is 10% of the current set with the potentiometer but it should be. That would give you with the dimming leads shorted, 10% of 3.35A or 335mA. That is going to do a lot less damage than 3.35 or 6.7A. You will need 2-3 units in series to get up to 24V before the driver will work properly. But even two in parallel should not be damaged with 335mA.



The B model does not have the internal adjustments. If you want both the internal and external adjustments, you want the AB model. There does not appear to be stock of these at american distributors at the moment.


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## Dave_H (May 21, 2020)

Dave_H said:


> Interesting article (though a bit older) dealing with 2 parallel case:
> 
> https://www.ledsmagazine.com/leds-s...ay-when-driving-multiple-led-strings-magazine



BTW not saying the method in this article is what the OP should necessarily use.

Not sure the probability of LEDs failing short but that could throw parallel balancing off quite a bit. Different modes of degraded operation are possible but self-destruct should not be one of them!

Likely there is an OTS parallel drive board/module which could balance currents or at least sense loss of string and reduce current or shut off; perhaps used in combination with multiple low-current drivers. 

An aside, I designed a discrete 48vdc/200mA linear regulator circuit for some LED strips with 14 series (2 parallel) times 3 (84 LED total) This could be driven by regulated 48v switching supply, common in telecom industry for IP phones. Measured vf total came in at 45-46v which left comfortable overhead, not much power loss (3v*0.2A = 0.6W). Considering the adapter is probably 90% efficient, overall efficiency of 80+% is not bad for this power level. Single-chip dc drivers are attractive but I wanted to customize some functions. For example, if the input voltage got too high (e.g. from using unregulated 48v "brick" adapter), it would switch to lower current to keep dissipation down, avoiding large heatsink on the MOSFET; or shut off completely.

Obviously the designers of those strips thought they could get away with that series/parallel arrangement; matched LEDs on the same PCB. Or maybe that's why I got them surplus for such a good price...

Dave


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## tedoro (May 21, 2020)

DIWdiver said:


> That Mean Well power supply looks perfect. It's a solid brand, and I agree, buy it from a distributor like Mouser, DigiKey, or others. I plugged it into Octopart, and it looks like Newark has the best price at $72.32. Check their shipping, though, as it could swallow most of that savings.
> 
> The first powerup is always scary. I'm coming up with no simple way to do it in stages.



Well, I guess I'll move ahead with this plan. I hearing its a big project, and has some juice running through it. I will take care. Many thanks for the help gentlemen. I will post with my result/further questions. T


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## JustAnOldFashionedLEDGuy (May 22, 2020)

Dave_H,


The majority of commercial and even residential fixtures are made with paralleled low power LEDs. We don't have the wide Vf variations we once had, though effective resistance is lower which makes things worse. COBs are already matched internally for Vf.


The reason why you parallel the LEDs first, then stack them in strings is it averages out differences better and mismatches are per parallel section, not on whole strings.


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## arek98 (May 22, 2020)

You could use something like this https://www.onsemi.com/pub/Collateral/NSI45060JD-D.PDF
They are $0.89 at DigiKey for example.
Look thru the spec (page 7 in particular)
You can connect it with LEDs directly to AC. Well thru the bridge .
You can use one bridge per connection point (all LEDs if they are plugged in one socket)
Then make a strings of LEDs in series with this device in each.
One goes to 100mA (you can adjust it with resistor between 60-100mA) but you can connect couple in parallel with one LED string to get more output. 
If you connect 3 those devices in parallel (see page 6) you can set any current between 180-300mA
Don't be scared by 45V rating at the beginning of spec, it is max voltage between anode and cathode of this part. It means that input voltage can't be higher than 45V from voltage dropped by LEDs.

For example, if you use 120V AC input, your LEDs are 9-12V I would put 10 of them in one string. Measure voltage, see how close it is to input, remove LED if is to high (LES are really droping 12V or more each) or add LED if is low and there is a space (e.g., you get 90V on 10 LED)

Edit: Adjustment resistor goes between pin 3 (Radj) and cathode (pin 4), value you get from Fig 6 on page 4 (0.125W resistor). Not connected pin or anything above 1000ohm gives 60mA output, about 7ohm for 100mA. Looks like 33ohm should give 80mA and 68ohm 70mA (these are common resistor values)


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## Dave_H (May 24, 2020)

arek98 said:


> You could use something like this https://www.onsemi.com/pub/Collateral/NSI45060JD-D.PDF
> They are $0.89 at DigiKey for example.
> Look thru the spec (page 7 in particular)
> You can connect it with LEDs directly to AC. Well thru the bridge .
> ...



Perhaps the OP can comment on whether he wants to take on driver design at the component level. Looks like a
small (or maybe not so small) PCB to mount these.

This is a linear device which brings a number of design issues including thermal management; and dealing with
line voltage requires correct component selection and safety issues e.g. fusing.

In my electronic design and component engineering experience over time, I find you really need to read
the datasheets and application notes carefully. For example maximum power per device is as low as 1.77W at
25C with minimal heatsinking (~1/2 sq. in. of copper), which for many cases is unrealistic and needs to be derated. At 
100mA, means limiting voltage drop across each device to below 17v including variations in line voltage. Minimum voltage 
across device is about 4v, below which current drops off. This adds up to a narrow window for number of LEDs in series. 
Actual vf of the LEDs needs to be accurately known (or at least measured) for given current; 9-12v is a wide range.

Not sure the device has thermal and short-circuit protection.

I don't want to recommend too many specifics but looks to me like pre-made properly-certified ac-dc CC drivers are
a strong approach. They offer flexibility, simplicity, efficiency, safety, and overall outweigh any benefits of linear
drivers for this level of power; and may cost less in the end.

And again, not objecting to linear drivers in some circumstances as noted from my 48v/200mA discrete design above. BTW
Infineon also has some linear CC devices for this type of use.

Dave


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## Dave_H (May 25, 2020)

arek98 said:


> You could use something like this https://www.onsemi.com/pub/Collateral/NSI45060JD-D.PDF One goes to 100mA (you can adjust it with resistor between 60-100mA) but you can connect couple in parallel with one LED string to get more output. If you connect 3 those devices in parallel (see page 6) you can set any current between 180-300mA Don't be scared by 45V rating at the beginning of spec, it is max voltage between anode and cathode of this part. It means that input voltage can't be higher than 45V from voltage dropped by LEDs. Edit: Adjustment resistor goes between pin 3 (Radj) and cathode (pin 4), value you get from Fig 6 on page 4 (0.125W resistor). Not connected pin or anything above 1000ohm gives 60mA output, about 7ohm for 100mA. Looks like 33ohm should give 80mA and 68ohm 70mA (these are common resistor values)


 Setting each CCR to 100mA (its max.) using 7 ohms will result in much lower RMS current (looks like 50% or less) because 100mA limit is peak current, and full-wave rectified ac results in pulsed output. Application note AND8433/D referenced from datasheet details this. Higher-output e.g. 160mA CCRs are available but still leaves a lot of limitations (and calculations); still need at least 3 in parallel. This will also result in 120Hz flicker which may or may not be an issue. This configuration is similar to LED Christmas lights, 60Hz flicker is visible (and sometimes disturbing), but 120Hz is better (my experiment by adding a full-wave bridge). Looks like using switching-type CC driver module is still a better approach. Dave


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