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LED Driver help pls >>>

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riley78

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Hi all ..

I have a high powered LED :

Forward Current @ Test: 1A
Forward Current If Max: 1.5A
Forward Voltage @ Test: 3.6V
Power Dissipation Pd: 5W
LED Mounting: SMD
Opto Case Style: SMD
No. of Pins: 5
Forward Voltage VF Max: 3.8V
LED / Lamp Size: 4.4mm x 4.4mm

What I`d like to know is do i need a driver or resistor, the LEDs mounted onto a PCPCB, I have a universal power adaptor with a voltage changer on it, which i dont think is adaquate its input is 230v~50hz 8.7w output 0 to 12v 300ma 3.6va(max).

I would be greatful if someone could point me in the right direction thnks
Pete
 
Your power adapter will drive your Led with a max current of only 300mA, at less than one-third of the LED's rated light output.

You will need a resistor rated to waste (12-3.6)*0.3 = 2.52W. Use a 5W resistor of (12-3.6)/.3 = 28Ω; a standard value is 27Ω.
 
With power LED's, you really don't want to use a resistor if you can avoid it. The best way to drive them is to use a buck converter with current sensing/control. Using a resistor is very in inefficient, especially with the supply voltage so far above the forward drop. As MikeMl has shown, your resistor will dissipate ~2.5 Watts as heat, while the LED only dissipates ~1 Watt. And most of that is not light that is being created, it will be heat. This is far from optimal.

With a buck converter though, you would be transforming the excess voltage into current, not wasting it as heat. The max amount of power you can get with your power adapter is basically 3.6 Watts, which at ~3.6 Volts will be ~1 Amp. And all of that will be going into the LED, not a limiting resistor. Mr RB's two transistor buck regulator with some tweaks can probably be made to do this. But I'm not 100% on this.

If I feel interested in the project I may decide to play with Mr RB's circuit and work something out for the OP.

Or I may design my own circuit from the ground up.

Or I may do nothing... who really knows. :D



Edit: Looks like Mr RB's circuit can't really be made to work sadly.
 
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Thanks for the reply guys,

I understand what your saying about not using a resistor, a bit of reading up i understand the differences more now, I have just purchased this driver, a friend told me it would be adaquate to run the LED, maybe you could take a look and give me your opinion.

https://uk.farnell.com/xp-power/ldu2430s1000/dc-dc-led-driver-constant-i-1000ma/dp/1738296

So the clear things up a bit, i have the LED on its correct PCPCB i have a adaquate heatsink, im hoping the above driver is ok, so im thinking all i need now is the right power adaptor with a power socket...

Ultimatly my goal is to power the LED thats all ...... if theres a easier alternative to all this im not seeing, id be greatful for feedback
 
Here is a schematic of a driver that works well enough in the sim for what you want to do. It's a very rudimentary buck topology current regulator.

View attachment 68525

Notes:
(1) The sim needs specific part numbers to work, the circuit it's self will work with most any generic parts though.
(2) The adapter must be able to supply ~1 Amp current for a moment for the system to start. Most wall adapters have a filter capacitor that will do this.
(3) V-Neg and V-Pos are labels replacing what would be wires. This was done to clean up the schematic. You MUST connect U1 to power for it to work.
(4) I am not perfect, I make mistakes. This circuit has only been simulated, it is not proven to work in real life. It's possible that it can not be made to work at all.
(5) The idea of the above circuit can be found in ready-built boards and IC's, you don't need to DIY if you would rather buy some thing that works.
(6) If you like this circuit, someone (Me?) can get you a BOM (Bill of Materials) from one of the major online suppliers so you can buy the parts needed.
(7) I TAKE NO RESPONSIBILITY FOR ANY INJURY OR DAMAGES RESULTING FROM ANYTHING I SUGGEST. IT IS YOUR RESPONSIBILITY TO DO THINGS SAFELY.

Attached is also the *.asc file for use with LTSpice III, should anyone want to investigate this circuit farther and possibly suggest improvements to the design.

Edit: Improvements are very likely as this is just a basic rough draft.
 
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hey oblivion thats fantastic.

ill take a better look at it tommorow with my friend..

if theres a ready built board available out there it would save me alot of time as im planning on producing a couple of these LEDs somewhere down the line..

out of intrest tho im intrested in building this project from scratch so if yourself or someone out there could send me a link to the parts needed again i would be greatful..
 
Pre-built power LED driver boards.

**broken link removed** is virtually identical to the circuit I provided. Though I'm not 100% certain it's pre-assembled.

**broken link removed** is the exact same kit as above, just cheaper. This one is almost certainly not pre-built.

**broken link removed** is another one, different site.

**broken link removed** is a really powerful unit.

**broken link removed** is another unit from parts express. good fit for what your doing.

*HERE* is another unit. Really cheap, and there are lots of pictures of what you're actually getting and reviews and stuff.
 
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Sorry, I only just noticed post number 4.

Those units are pretty much the exact same circuits as above, only they are put inside enclosed plastic boxes and they give you a way to control brightness externally.

How to use.
The chart for how to use those units is on the bottom of page 2 of the datasheet. Plus the pictorial showing the pinout for your specific unit. You control the brightness with a 2M Ohm potentiometer connected from the control pin to -Vin.


I have aggregated all the most important information you need to know to be able to light your LED into one single picture for your reference here...

View attachment 68555
 
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hey thnks for the help.

I dont realy need a potometer for brightness contol I just need the LED to come on, would your diagram still work without the pot.

My LED came in post today, im a bit upset as its not solded to the PCPCB board, iv been watching a couple of vids on youtube on how to manualy do it myself as its such a small area to solder and i just havnt got the tools to do it, so now im searching the web for the same LED but already on the board, and i just carnt find one... HERES ONE but its sold in bulk only..

https://uk.mouser.com/ProductDetail/LedEngin/LZ1-30DB00/?qs=vmkU9SbkviScplRglSS7/GzR8N%2bBQq1D

the whole projects turning into a headache, am almost at giving up point ... but thanks for the diagram it`ll come in very handy.
 
another thing thats bothering me is the driver mentioned above that i have puchased has a output Voltage of 2v-28v where my LED only needs 3.6v-3-8v, will my LED only draw voltage it needs, also driver is rated 24w where my LED is only 5w, im not sure whether this matters either..

i dont want to chance anything seeing as the LED was quite expensive..
 
another thing thats bothering me is the driver mentioned above that i have puchased has a output Voltage of 2v-28v where my LED only needs 3.6v-3-8v, will my LED only draw voltage it needs, also driver is rated 24w where my LED is only 5w, im not sure whether this matters either..

i dont want to chance anything seeing as the LED was quite expensive..

Good LED drivers are constant current. If your driver is set for 1A it will hold at 1A for any LED (LEDs) that have a voltage drop of 2 to 28V. So your LED will get 1A and have 3.7V across it. If you have two LEDs (in series) the driver will output 1A and 7.4V, or three LEDs = 1A and 11.1V etc up to ten LEDs -1A and 37V.
 
riley78 said:
I dont realy need a potometer for brightness contol I just need the LED to come on, would your diagram still work without the pot.

You would either leave pin three (the green wire) unconnected, or short it to -Vin for full brightness. I don't know which. Most likely leave it unconnected.

riley78 said:
will my LED only draw voltage it needs[?]

(Edit: ronsimpson beat me to it.)

You could say that. The driver should only provide a max of 1 Amp current to the LED at full brightness. It's the driver that decides this though, not the LED.

The best way to play safe would be to use some other load (such as a 12V light bulb or physically large resistor) and an Amp meter on the LED side and use a pot. Then you will know exactly how it will behave without risking your really expensive LED.

riley78 said:
My LED came in post today, im a bit upset as its not solded to the PCB

Surface mount soldering is not all that difficult if you know what to do. And a little bit of practice goes a long way. One thing to worry about with surface mount LEDs though is that it can be easy to over heat them by heating the part for too long. Power LEDs being really big makes this less of a danger. Heat sinking and temperature controlled irons make this an after thought altogether.

The main things for soldering in general are...
(1) The solder points need to be clean, most important is cleaning off corrosion/oxidation.
(2) The heat needs to be just right. Cold joints and over heating are big problems.
(3) Use a good clean iron, with the right Wattage for the job. (25-45 Watts probably)
(4) Use the right solder. Rosin core solder only. *NOT* metal/acid core/jewelry solder.
(5) Try to use flux paste whenever you can. Makes point (1) less important.

And the steps I use for surface mount soldering are roughly...
(1) Lightly clean all solder points. Fine emery boards work well for this. Wash with alcohol and Q-tips.
(2) Apply a light coating of flux to the boards solder location (known as a "pad").
(3) With a clean and well tinned iron, heat the pad until the flux begins to boil.
(4) Apply the solder to the pad lightly where the iron touches the metal of the pad, until the pad is well tinned.
(5) Remove the solder, then remove the iron. Let the solder cool without disturbing it. Don't blow on it to cool it faster.
(6) Do steps (1) through (5) for all solder joints, until all parts and the board are tinned cleanly.
(7) With all the pads/parts tinned. Clean again, this time with just alcohol and Q-tips. And apply fresh flux paste.
(8) Carefully align the part over the pads, it should slightly stick to where you put it because of the flux.
(9) With a tooth pick in your left hand, and the iron in your right, reheat all the solder joints.
(10) Keep doing (9) for all the pads while carefully nudging the part into proper alignment with your left.

If all goes well, you should have a surface mount part cleanly soldered to your board.
 
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