Trying to Find Driver for LED light.

Thread Starter

woozycactus

Joined Jan 4, 2021
95
Hello,

I have made a special LED light. it has 176 3W LEDs. Each one needs to be driven at 3.3 volts and 350ma. I would prefer to keep it under 50volt input but cannot find a reasonable power supply that's not physically too big. Any recommendations? Otherwise. My most reasonable circuit design would be to run on 120vac with a series-parallel config. My questions are, is this safe? If the LED pins are exposed, can you get a shock from them, or will all the exposed pins be at the 3.3ish volts? will the first and last pins in series be any different than any others? I can protect the high volt connections and components including the bridge rectifier but not the LEDs. Any insight will be appreciated and just need to know about this. everything else I have already designed.

thanks, in advanced!

PS here is link to LED circuit layout for 120 volt. Its just the LEDs and resisters.

https://ledcalculator.net/#p=120&v=3.3&c=350&n=176&o=s
 
Last edited:

BobTPH

Joined Jun 5, 2013
4,906
What are you lighting with it? That is a lot of light considering that 5 of them should be should produce the light of a 100W incandescent bulb.

Except that 3.3V and 350 mA is only 1.15 W. So they are more likely 1W LEDs. Still, at 1W each that is about 12 100 W bulbs.

As for using line voltage, no, you cannot do that if the pins are exposed, and you don’t know enough th do it safely.

If you really need to do this get 12 constant current supplies at 350 mA and 50V max output and run a series string of 15 on each.

Bob
 

Thread Starter

woozycactus

Joined Jan 4, 2021
95
What are you lighting with it? That is a lot of light considering that 5 of them should be should produce the light of a 100W incandescent bulb.

Except that 3.3V and 350 mA is only 1.15 W. So they are more likely 1W LEDs. Still, at 1W each that is about 12 100 W bulbs.

As for using line voltage, no, you cannot do that if the pins are exposed, and you don’t know enough th do it safely.

If you really need to do this get 12 constant current supplies at 350 mA and 50V max output and run a series string of 15 on each.

Bob
Does it matter?

Under driving the lights for longevity.

I don't know enough to do it safely? who are you to judge what I do and don't know? You dont know my background..

not using 12 power supplies, that's dumb when I can just use a 50v 5amp supply.... but I don't want a power supply as big as a dictionary...
 

BobTPH

Joined Jun 5, 2013
4,906
I don't know enough to do it safely? who are you to judge what I do and don't know? You dont know my background..
I beg to differ. The question you asked is enough to know that.

Yes, you could use a single 50 V supply but additional electronics are needed. Driving high power LEDs without constant current is a poor practice you will find in cheap Chinese products but not in reliable UL approved ones.

Bob
 

Thread Starter

woozycactus

Joined Jan 4, 2021
95
I beg to differ. The question you asked is enough to know that.

Yes, you could use a single 50 V supply, but additional electronics are needed. Driving high power LEDs without constant current is a poor practice you will find in cheap Chinese products but not in reliable UL approved ones.

Bob
15 years working with high voltage, I don't specialize in LEDs. However, the application for this build needs to run resistors. No other choice which is why I'm asking the questions that I am and one of the reasons we are using 3-watt LEDs and under driving.

The correct non arrogant response would be, no you would have high voltage at the exposed LED pins and would need to be covered... I have already built one protype with 95 LEDs at 36-volt supply and it's not enough. I can't find a power supply to run this below 50 volts, which is the max recommended safe voltage for dc, that will fit into the housing.

The build is for production, so it is what it is. I would love to be able to cover them, but the heat is going to warp acrylic and they don't want glass on set.

The only other option i know is to use 2 of the 36-volt power supplies but trying to stay away from that if possible..

If you know the answers to the questions. I would appreciate it if you shared them. If not, then thanks for trying. I can cover some of the exposed pads if needed.
 

dendad

Joined Feb 20, 2016
4,134
It is unfortunate that you replied in such a manner to @BobTPH 's answer to your query @woozycactus. He is really trying to help.
You yourself stated ...
I don't specialize in LEDs
What @BobTPH says is correct.
It is really unwise to just rely on series resisters when driving LEDs. particularly high power ones. The recommended way is to use a constant current supply. And a switch mode constant current supply will run a lot cooler than a series resistor, and more efficiantly, so your main power supply can be physically smaller.
I would stress that running them directly from the mains is quite dangerous.
The build is for production,
Does that indicate you are building this for customers? If so, it is extra important that you do it safely.
Having multiple small constant current LED drivers, each driving their own string of LEDs is a real good idea as then you will have some built in redundancy if some LEDs fail. That way you do not loose all the LEDs. And if you just use series resistors, having some of the LEDs fail short circuit can avalanche to take all the LEDs out.
LEDS are current devices and should not be thought of as 3.3V lamps. This is a common error we see on this forum over and over again.
Most of us are here to help, and many of us have 50+ years in the electronics industry. I have spent years in high power HF radio transmitter station operation and then in designing and building industrial control systems. In both these fields, a big aim is safety and reliability.
I am not the only one here with reasonable experience. We are here to help.
 
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Thread Starter

woozycactus

Joined Jan 4, 2021
95
It is unfortunate that you replied in such a manner to @BobTPH 's answer to your query @woozycactus. He is really trying to help.
You yourself stated ...

What @BobTPH says is correct.
It is really unwise to just rely on series resisters when driving LEDs. particularly high power ones. The recommended way is to use a constant current supply. And a switch mode constant current supply will run a lot cooler than a series resistor, and more efficiantly, so your main power supply can be physically smaller.
I would stress that running them directly from the mains is quite dangerous.

Does that indicate you are building this for customers? If so, it is extra important that you do it safely.
Having multiple small constant current LED drivers, each driving their own string of LEDs is a real good idea as then you will have some built in redundancy if some LEDs fail. That way you do not loose all the LEDs. And if you just use series resistors, having some of the LEDs fail short circuit can avalanche to take all the LEDs out.
LEDS are current devices and should not be thought of as 3.3V lamps. This is a common error we see on this forum over and over again.
Most of us are here to help, and many of us have 50+ years in the electronics industry. I have spent years in high power HF radio transmitter station operation and the in designing and building industrial control systems. In both these fields, a big aim is safety and reliability.
I am not the only one here with reasonable experience. We are here to help.
When someone replies with arrogance, I'm going to reply in such a way. I know how LEDs work, I know how they should be driven. I understand the risk in using just resisters. It's a disposable build that is not being sold and being done a favor to someone who knows that's it not going to be 100% reliable or safe. However, they don't want a glass cover and don't want someone to get bit by just touching it. That's the concerns. I asked specific questions regarding and get replied with a statement that is as if y'all know me.

And to add, if y'all don't feel comfortable with answering the questions I'm asking or don't know the answers, feel free to say so and I'll spend the time wasting material to experiment. No hard feeling, just shouldn't assume someone is incompetent..
 
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Boggart

Joined Jan 31, 2022
13
I think you need to take it down a notch, attitude-wise, the questions you asked did imply a lack of knowledge. For example, asking if a string of LEDs connected directly to mains power will all be at 3.3V, that shows you don't understand how voltages work in reference to ground. If you do understand that, it's an odd question to ask, because obviously the LEDs at the top of the string (closest to the active/line) will be at mains voltage, with that voltage steadily decreasing through the string.

You don't drive power LEDs with resistors, you can, but it's crude, there are "smart resistor" ICs which are a simple constant current driver IC, they just have two pins and you use them like a resistor, just get them the right way around and make sure you heatsink them and don't exceed their ratings. The NSI50350 (350mA, 50V max) is a good example of such an IC and they are cheap.

Anyway, if you want to do this safely and avoid ending up getting sued or charged with causing injury through negligence or whatever, you need fully isolated LED drivers. Go to the Meanwell website and find an appropriate driver or drivers (I agree that splitting the LEDs into several strings is a very good idea) and aim for a LED string voltage of less than 48 volts or so for safety. Lower is better, you can get bitten from lower voltages if you have damp fingers and bridge both ends of the supply.

And, once you are done connecting everything, coat the LED connections in a conformal coating to add a level of insulation, there are spray/brush on conformal coatings that are designed for this sort of work.
 

Thread Starter

woozycactus

Joined Jan 4, 2021
95
I think you need to take it down a notch, attitude-wise, the questions you asked did imply a lack of knowledge. For example, asking if a string of LEDs connected directly to mains power will all be at 3.3V, that shows you don't understand how voltages work in reference to ground. If you do understand that, it's an odd question to ask, because obviously the LEDs at the top of the string (closest to the active/line) will be at mains voltage, with that voltage steadily decreasing through the string.

You don't drive power LEDs with resistors, you can, but it's crude, there are "smart resistor" ICs which are a simple constant current driver IC, they just have two pins and you use them like a resistor, just get them the right way around and make sure you heatsink them and don't exceed their ratings. The NSI50350 (350mA, 50V max) is a good example of such an IC and they are cheap.

Anyway, if you want to do this safely and avoid ending up getting sued or charged with causing injury through negligence or whatever, you need fully isolated LED drivers. Go to the Meanwell website and find an appropriate driver or drivers (I agree that splitting the LEDs into several strings is a very good idea) and aim for a LED string voltage of less than 48 volts or so for safety. Lower is better, you can get bitten from lower voltages if you have damp fingers and bridge both ends of the supply.

And, once you are done connecting everything, coat the LED connections in a conformal coating to add a level of insulation, there are spray/brush on conformal coatings that are designed for this sort of work.
The issue is when someone says, you can't do this because you don't know how to do it safely, to someone you don't know, is an insult and arrogant.

I understand it's crude, other options have been. Explored, I don't know about the IC you are talking about but every normalized option has caused issues which is why resisters are being used, I've already said our best option was to go under 50 volts but I cannot find a powersupply to fit in the housing with that kind of output.its going to be used daily for about 20 mins daily for maybe 6 months and then it's going into the trash. I can sit here for hours and experiment with it to see what the voltages are at every exposed pin, figured I would ask before wasting bunch of time. Using multiple supplies would work best but again, not enough space. The best I have come up with is use mains, rectifier, smoothing and cover the exposed high volt with epoxy but idk what the epoxy or other coatings will do with the heat. It's alot of heat in a small space.

This needs to be analog, no switching, no pwm, no dimming, nothing. Just drive the LEDs with a direct current.
 
Last edited:

Boggart

Joined Jan 31, 2022
13
Ok, well really not sure what to say about "going into the trash", I hope that just means it's going to a local e-waste recycler.

That aside, heat is the enemy of LEDs, if you don't have half decent thermal management, they won't last long, you can't put a heap of LED power into a small space with no thermal management, the LEDs will overheat and fail (the LED die usually unbonds from the die cup, so the LED goes open circuit).

If this were me, and I only wanted to use resistors for simplicity, then I'd just do this:

Basically, the resistor required for each string of LEDs is: (Supply voltage-LED string voltage)/LED current.

So, for example, using 48 volts (a common power supply voltage), with LEDs with a forward voltage of 3V (which is more typical nowadays for whites etc), you might do strings of 12 LEDs, giving (48-36)/0.35=34 ohm (use the next common value up, 39 ohm, or go down slightly to 33 ohm).

As a power rating, you multiply the resistor voltage drop (12V in this example) by the string current to get 12x0.35=4.2W. Double that and use a 10W resistor.

This still gives a lot of power wastage in the resistors, which is why I suggested the ICs, they let you use string voltages much closer to the supply voltage as they only need 3V or so for 80% of full regulation current. But, the 12V across the resistor allows for a lot of LED voltage variation etc.

It's just a matter of doing the calcs...
 

Thread Starter

woozycactus

Joined Jan 4, 2021
95
Ok, well really not sure what to say about "going into the trash", I hope that just means it's going to a local e-waste recycler.

That aside, heat is the enemy of LEDs, if you don't have half decent thermal management, they won't last long, you can't put a heap of LED power into a small space with no thermal management, the LEDs will overheat and fail (the LED die usually unbonds from the die cup, so the LED goes open circuit).

If this were me, and I only wanted to use resistors for simplicity, then I'd just do this:

Basically, the resistor required for each string of LEDs is: (Supply voltage-LED string voltage)/LED current.

So, for example, using 48 volts (a common power supply voltage), with LEDs with a forward voltage of 3V (which is more typical nowadays for whites etc), you might do strings of 12 LEDs, giving (48-36)/0.35=34 ohm (use the next common value up, 39 ohm, or go down slightly to 33 ohm).

As a power rating, you multiply the resistor voltage drop (12V in this example) by the string current to get 12x0.35=4.2W. Double that and use a 10W resistor.

This still gives a lot of power wastage in the resistors, which is why I suggested the ICs, they let you use string voltages much closer to the supply voltage as they only need 3V or so for 80% of full regulation current. But, the 12V across the resistor allows for a lot of LED voltage variation etc.

It's just a matter of doing the calcs...
How do the chips work? Do they pulse?
 

BobTPH

Joined Jun 5, 2013
4,906
You said:

My most reasonable circuit design would be to run on 120vac with a series-parallel config. My questions are, is this safe? If the LED pins are exposed, can you get a shock from them, or will all the exposed pins be at the 3.3ish volts?
I don’t care how much experience you have, this question proves you do not know how to work with mains voltage safely.

I was not being arrogant, just stating the obvious.

Bob
 

Thread Starter

woozycactus

Joined Jan 4, 2021
95
You said:


I don’t care how much experience you have, this question proves you do not know how to work with mains voltage safely.

I was not being arrogant, just stating the obvious.

Bob
Now you're just trying to start crap. I'm not buying into your arrogance and stupidity, you can leave the thread now.
 

BobTPH

Joined Jun 5, 2013
4,906
There is a report button on each post that allows you to complain to a moderator if you feel that I have broken forum rules.

Bob
 

Wendy

Joined Mar 24, 2008
22,841
My personal feeling is the TS needs to stop and read up on some of the basic math, for example I have written a articles to help beginners with LEDs.
LEDs, 555s, Flashers, and Light Chasers
There was a time not too long ago that we did not even allow discussions of LEDs to mains. Unless you put in the homework, as in reading up on LEDs I see no way that you can do this safely. You asked for advice, no one said you had like the advice you were given.
 

BobTPH

Joined Jun 5, 2013
4,906
So it sounds like this is a prop.

If you can run a 120VAC line into the device, why can you not run a 48V line and have the power supply remote? Inside you could could use 12 LM317s as current regulators running 1A to each of 12 series strings. You could even put the drivers outside and use a 13 wire cable.

And this is what I was talking about when I suggested 12 constant current drivers. Is it too large?

Bob
 

DickCappels

Joined Aug 21, 2008
8,710
I have made a special LED light. it has 176 3W LEDs. Each one needs to be driven at 3.3 volts and 350ma. I would prefer to keep it under 50volt input but cannot find a reasonable power supply that's not physically too big. Any recommendations? Otherwise. My most reasonable circuit design would be to run on 120vac with a series-parallel config. My questions are, is this safe? If the LED pins are exposed, can you get a shock from them, or will all the exposed pins be at the 3.3ish volts? will the first and last pins in series be any different than any others? I can protect the high volt connections and components including the bridge rectifier but not the LEDs. Any insight will be appreciated and just need to know about this. everything else I have already designed.

thanks, in advanced!
Clearly, from the text in bold you should not take the risk of running this from over about 40 volts DC and 36 volts AC. Otherwise not only can you get shocked but you can get dead. Please also consider fire and personal safety by keeping any metal parts with which any person can make skin contact cooler than 60°C (140F) and voltages, and we always include a fuse at least in the primary circuit.

By the way, the large LED arrays I have made photo therapy were powered by 24 volt laptop power supplies. I try to use these well engineered and safety approved power supplies because others have already gone to a lot of trouble to make a safe power supply so I can concentrate on "my part" of the project.

Another great benefit to using pre-made power supplies is that they are often regulated. That takes the normal variation in line voltage out of the picture and I can use most of the voltage across the LEDs and very little is spent heating up resistors.
1650886696459.png

Solutions were given in this thread that can allow you to power your light safely. Please care for yourself, your friends, and your family by being careful to follow that advice.
 
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