Advice on SMD LED types - General Electronics - Arduino Forum

UKHeliBob:
I have moved this query to a more appropriate section of the forum

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Thank you Bob.

The project is to convert some nasty repro (all that is now available) into LED.

Some pictures of my quick lash up...

The LEDs in my lashup are Ebay specials running at 20mA. The brightness of the ones fitted I would say is a little higher than the stock 5W bulb in there, but I have taken no measurements.

I now have to lashup the indicator side (as they are not BMW parts. ) and have to bear in mind the filtration of the lens. There would normally be a 21W incandescent in there. My initial thought was 14 of the same LEDs at the same current, but I am waiting for new stock to arrive. I could use Amber LEDs but they are typically 20% of the output of white ones. I realise there will be a loss through the lens, so not sure which option is the more sensible.

In order to produce a production unit, I will design some custom PCBs and then switch to SMD LEDs. Hunting around for something suitable has given me brain ache. The problems I think that I have are:

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Additional reading:
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Varying output units, some in mCd others in LM. I think that the LEDs I have in there now are 5Cd but from looking at specifications of SMD, it looks like that can't be the case at 20mA.

Various case sizes. I looked at which are easy to handle but then read that they are triple emitter and want lots of current. They may as a result be far too bright and not diffuse enough. Then I looked at cases which would prototype onto stripboard well, but Farnell claims that most of the options are all out of stock or discontinued, although I thought that was fairly new?

Getting a similar or slightly higher output than incandescent without producing half a dozen bright beams, instead of a diffuse light that iluminates the lens nicely. The discrete LEDs are obviously such when lit, but it isn't that objectionable. They are still quite narrow angle though.

In a nutshell, can somebody please educate me?

IMO, install LEDs that you know will be brighter than you need, and then tune them to the desired brightness by changing the resistor values and/or disabling some of the LEDs.

I would probably get ebay/aliexpress SMD 's, they have 3 LEDs in a 5mm x 5mm package for the SMD version, 20mA/LED at full brightness (added bonus that if you wire them that way, you could turn off one - or even two - leds in every package to evenly distribute the reduction in brightness.

White LEDs behind amber filter are generally brighter than amber LEDs in the same circumstance - but you might be able to get it bright enough anyway without much difficulty, and would be rewarded for the amber LEDs with a more saturated color.

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garvind25

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SMD LED size for beginners

« on: September 10, , 03:48:56 pm » Hi,

  This is the first time I will be using SMD LEDs for a project. Can anyone suggest a size of LED which beginners can start off with.

Thanks,
Arvind Gupta

stmdude

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Re: SMD LED size for beginners

« Reply #1 on: September 10, , 03:57:48 pm » There's so much information missing here..

Have you worked with SMD components before?  If so, what sizes?

Do you want/need RGB diodes?  Is the intensity of the light a factor (bigger LEDs = More light) ?

I'll use myself as an example. I'm working with components all the time, and thinking of going to . However, I'm using LEDs, as I like the amount of light coming from them (not quite as "sharp" as s).

If you have good eyes, you could probably solder without a microscope. The following users thanked this post: garvind25

garvind25

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Re: SMD LED size for beginners

« Reply #2 on: September 11, , 06:46:03 am » Thanks for you reply. Intensity of light is not a factor-- using LEDs as indicators only; though lesser the current the better (about 8 to 10 mA). Colour-- the one which has minimum voltage drop; I suppose it is red colour. Yes I have soldered OP07 smds before.

Regards,
Arvind Gupta

Kjelt

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Re: SMD LED size for beginners

« Reply #3 on: September 11, , 07:54:53 am » Indicator only then it does not matter much. I like the personally since they also fit snugly between TH prototype board pads, so they can be use also for normal prototyping.
If you only want it for SMD pcbs then are good.

Voltage drop and color:  http://www.lumex.com/article/led-color-guide

Note that the human eye is the most sensitive to green so although it has a slightly higher voltage drop you need less current to make it more easy to detect by the human eye. The following users thanked this post: ratio, garvind25

grifftech

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Re: SMD LED size for beginners

« Reply #4 on: September 11, , 06:03:39 pm » biggest one you can find The following users thanked this post: ludzinc

stj

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Re: SMD LED size for beginners

« Reply #5 on: September 11, , 07:33:00 pm » so 's then! 

suicidaleggroll

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Re: SMD LED size for beginners

« Reply #6 on: September 11, , 07:52:12 pm » I typically use your typical green LEDs for indication, eg:
https://www.digikey.com/product-detail/en/wurth-electronics-inc/VS/732--1-ND/

Feed it 0.1-1.0 mA and you're set.  They get a little dim running at 1.8v, but you can still see them clearly, and at 2.5V or higher drive voltage with the resistor sized for around a milliamp they're more than bright enough.

If you're not comfortable soldering then you'll want to go larger, naturally.  We don't know what your capabilities are. « Last Edit: September 11, , 07:56:00 pm by suicidaleggroll »

NivagSwerdna

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Re: SMD LED size for beginners

« Reply #8 on: September 11, , 08:14:10 pm » So many choices... e.g. look at http://www.kingbrightusa.com/category.asp?catalog_name=LED&category_name=KCSMD+LED

For single colour SMD boring LED... (very standard on Arduino boards or the like) or (very standard where tight for space).

The dual LEDs are rather nice too...

Small things eg tend to be much cheaper.

alank2

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Re: SMD LED size for beginners

« Reply #9 on: September 12, , 02:58:44 am » I tend to use sized parts because they are easier to work with.  If I need to make something smaller, then I'd go smaller.

garvind25

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Re: SMD LED size for beginners

« Reply #10 on: September 12, , 02:31:00 pm » Thanks for all your replies. I suppose being a rookie, I will stick to size. As far as colour is concerned, I will will go for red (as the cheap PCBs have green colour finishing). Just 2 more things:

** How much current should I feed a red LED. I suppose 1-2 mA will be quite less.

** In eevblog forum, once I have seen a post, how do I get back to it again. I couldnt find a link which indicates 'my posts'/ 'my recent activity' etc. Presently, I have to rewind myself to remember in which forum topic I had posted my query and then search the list. It takes quite an effort

Again, thanking all,

Arvind Gupta.

stj

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Re: SMD LED size for beginners

« Reply #11 on: September 12, , 03:26:38 pm » datasheets are your friend here,
different leds produce different output for the same current.
KingBright is probably the company that you will run across the most.
all the sellers stock them.
http://www.kingbright.com/

garvind25

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Re: SMD LED size for beginners

« Reply #12 on: September 12, , 03:50:38 pm » OK thanks. I checked the kingbright site for IV curves of SMD LEDs for and red colour. The current required seems very high for 2 v drop across led.

/ --> 30 mA for 2v

So I suppose thats too high ! Pls. help (or maybe something is wrong in my understanding).

link --> http://www.kingbright.com/attachments/file/psearch/000/00/00/KPHCM-SURCK(Ver.12A).pdf
link ---> http://www.kingbright.com/attachments/file/psearch/000/00/00/KPT-SURCK(Ver.19A).pdf

Regards,
Arvind Gupta

alank2

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Re: SMD LED size for beginners

« Reply #13 on: September 12, , 03:54:52 pm » My favorites for reasonable current are APTCGCK and APTSURCK.

Then there is the HELI2 series from kingbright, all have 2mA current listed for the test condition:

https://www.digikey.com/products/en/optoelectronics/led-indication-discrete/105?k=&pkeyword=&s=&FV=ffe&mnonly=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=100

DaJMasta

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Re: SMD LED size for beginners

« Reply #14 on: September 12, , 04:30:29 pm » Though you have plenty of input:

I've sort of standardized around parts because they're a nice mix of inexpensive, small, and still fine to work with by hand.  LEDs tend to be just a bit more challenging than other parts of the same size (usually the pads on the end are a tiny bit smaller and you always have to remember how their polarity is marked on the top side  ), but are still plenty doable by hand.  You run slightly higher risk using smaller and smaller parts in that you can't heat them for as long while soldering, but honestly, it's pretty rare that you have to apply heat for very long to an SMD part, and I can't remember the last time I burned out something with just the iron.

For indicators, I also end up using 5mA or less, usually... and blue/white LEDs, with their much higher voltage drop, often need considerably less to not stick out like a sore thumb.  Red/orange LEDs are great for low voltage, low current operation, but sometimes you just need more than one color.

Ian.M

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Re: SMD LED size for beginners

« Reply #15 on: September 12, , 04:31:42 pm » Forum navigation:
At the top, just below 'Hello '
you will see 'Show new replies to your posts.'  Click it for a list of UNREAD replies to your posts.   If you need to go back to something you posed to but have already read, goto your profile and use show posts, find the last post you made to the topic in question and click the link to get back to the actual topic.   If you need to 'bookmark' a post to reread and don't want to reply you can simply use the button to thank it, as show posts also has a section for stuff you've thanked.

Many SMD LEDs are excessively fragile if hand soldered, and really need  reflowing with a well controlled temperature profile for reliability.  It is possible to hand-solder many packages but even slight pressure on the package when its hot can result in failure, and manual hot air reflow may cook the LED.  Damaged bond wires may not initially cause a problem if they are still making contact but may cause the LED to start blinking due to intermittent contact, or fail totally a considerable time later.  As such whenever manual assembly is a requirement its worth choosing a package and laying out the board for easy assembly - extra pad length so you've got room to get the iron tip on it without nudging the LED, and try to avoid small packages, and ones that have a substrate heatsinking pad under the package. The following users thanked this post: NivagSwerdna

suicidaleggroll

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Re: SMD LED size for beginners

« Reply #16 on: September 12, , 06:56:37 pm »

OK thanks. I checked the kingbright site for IV curves of SMD LEDs for and red colour. The current required seems very high for 2 v drop across led.

/ --> 30 mA for 2v

That's the absolute maximum current, you need considerably less than that to turn it on.  I would start with 1mA, but buy a few extra resistors of different sizes in case you want to go brighter/dimmer.

Kjelt

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Re: SMD LED size for beginners

« Reply #17 on: September 12, , 09:36:41 pm » Use a low ohm resistor say 100 ohm in series with a ten turn trimpot of 2k or 5k ohms in series with your led and see which brightness you like, then measure the total resistance and take the first E12 value that comes nearest to that.

westfw

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Re: SMD LED size for beginners

« Reply #18 on: September 14, , 06:35:44 am » I bought a bunch of resistors and PLLC2 LEDs when I was first contemplating using SMT, and while they're pretty easy to solder, I find them to be depressingly "not any smaller than 0.1in TH components" (vertically mounted resistors, or 3mm LEDs) when it comes to PCB footprint.  So more recently I've been working with components, which seem to be a better compromise.

As for current, most LEDs are still RATED for 20 to 30mA, even though they're much brighter than the 30mA LEDs of 40 years ago.  For indicator LEDs... I usually throw 1k resistor in series (3-5mA current) with LEDs (mostly because I'm a big believer in using lots of same-value components), and that's plenty to too-much for any modern LED.  There are a bunch of development boards (TI Launchpad!) where I've drawn over the LEDs with sharpie, because they're painfully bright otherwise... 
One thing to watch out for is power rating of the resistors - 30mA through a 100ohm resistor is 0.09W, which is a little close to the max rating of 0.1W for a typical resistor.

mariush

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Re: SMD LED size for beginners

« Reply #19 on: September 14, , 06:45:40 am » Also don't forget to check out the VIEWING ANGLE

A very narrow angle will make your led behave like a laser pointer and burn the person's eyes   Could be desired if you have for example light guides  / light bars / light pipes

Otherwise for simple indication (on/off , etc) you may want wide viewing angle.

Kjelt

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Re: SMD LED size for beginners

« Reply #20 on: September 14, , 06:48:56 am »

One thing to watch out for is power rating of the resistors - 30mA through a 100ohm resistor is 0.09W, which is a little close to the max rating of 0.1W for a typical resistor.

is usually 0,05-0,06W power rating however half their body is drowned in solder which is a great heatsink so I always wonder how far one can get away with that 
For reliable long life designs I would definitely stick to the power rating,use two resistors in series if necessary or larger ones.