High power LED Ledengin 10W. How can I drive 4+1 of these from a laptop power supply?

Dear fellow hobbyists,
I have four deep red, 10 watts Ledengin bulbs mounted on a MCPCB (as well as one cool white 10 watts bulb from the same company). I would like to bring them to life using a laptop power supply. I know that I do absolutely need a constant current to avoid getting SEDs or friods. Unfortunately my knowledge of circuits is very basic and several decades old. I have read and re-read several times the excellent instructubles tutorials and gathered more information from the web. I think I got it (well…sort of) and I have successful built a small array of inexpensive, low power (20 mA) LEDs, using a resistor as the current limiting device. However I am aware that this is a rather inefficient way to feed high power LEDs, particularly related to power dissipation (i.e. efficiency of the circuit). I would like to build a LED driver using either 1) the NFET + NPN circuit #2 from Dan (https://www.instructables.com/id/Circuits-for-using-High-Power-LED_s/) but I am not sure if the listed components are good enough to drive four/five 10W LEDs (mid power LEDs are used in the example), or 2) find a buck pack that does not cost a fortune and is guaranteed to work (National semiconductors seems to have a few at very low prices, such as …., but I am not sure they will do the job and how well) . Also, I would like to know if it is possible to drive the 4 red together with the 1 white LED from the same power supply, or if it is better to use two PS, each with its own driver? The two ledengin LEDs are LZ4-00R210 for the red and LZ4-00CW10 for the white bulb. I intend to drive them at 700 mA to maximize shelf life and the maximum Vf for this current are 13.76 V for the red (only one bin code) and 16.64 V for the white (for safety I was advised to use the highest Vf bin value from the datasheet as it is close to impossible to get the correct bin code specific for the bulb from the distributor). I am actually considering running the 4 red + 1 cool white LEDs all in parallel, with each individual LED having its own current limiting device (the inexpensive ones from Dan): a bit more involved but maybe the safest?
Thank you in advance for all the help you can give me.
Arcibaldo

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I'd always try and run LEDs like that in series - but then you'll need a supply that can feed 14 x 4 + 17 or 73 Volts.... Any passive current control is going to be inefficient compared to a switcher design, If you haven't got the electronics background, and you want to go to switchers, you'll have to buy a buck-puck. You could use LM317s as current regulators, and they'd not be too bad dissipation wise, on an 18V laptop PSU, dissipating 4*.7*4 11Watts and 1W red and white respectively. Efficiency would be a shade over 75% - ignoring the laptop supply, With a good buck-puck you could be in the low 90's percent. Steve
arcibaldo (author)  steveastrouk8 years ago
Thank you Steve, very good advice. Buck-pucks though cost quite a few bucks (above 10 $)and I was wondering if the following circuit is possible. I remember there being an issue with feeding LEDs in parallel with the current not being exactly constant, but wouldn't one regulator/one LED take care of the problem? Also wouldn't I be able to use a mixture of different LED (with different Vf) with this setup? Again, sorry for my all encompassing ignorance and the crudeness of my drawing (powerpoint....) Thanks again Acibaldo
C1.jpg
Sorry, should have been more explicit myself - that's what I meant ! 317s wont take more than 35 volts input, so you can't really series connect the leds. It'll work fine, but your Red leds are going to dissipate nearly 3W each - make sure they have good heatsinks. Steve
arcibaldo (author)  steveastrouk8 years ago
thank you Steve! I am really happy to find that my circuit stands a chance. I would really like to avoid burning the LEDs at over 30$ each... One more question, sorry. Will the LM317 dissipate a lot of power too? Is advisable to add heat sinks for them as well? Arcibaldo
ARGHHH ! Sorry archibaldo - that was sUPPOSED to be the 317s not the "Red leds" ....you leds should be pushing 10W dissipation each ! Steve
PS test each circuit with a 17/0.7 = 20 Ohm resistor BEFORE you put the LED in ....
arcibaldo (author)  steveastrouk8 years ago
Thank you for the clarification, Steve. And thanks for the advice to test the circuit PRIOR to adding the LED.... Will attempt sometimes in the future... keep you posted with the results. In the meantime: much obliged! Arcibaldo
Hello arcibaldo,
if you are still looking for a driver: I use 3 channel 1000mA constant current driver from german company PCB components.
They are suitable for the RGB and RGBW/RGBA Ledengin 10W Leds and for Lamina ceramics Titan RGB.
The ledengin can be driven with up to 1400mA as long as the temperature at the LED remains low (app. 60..70°C is fine).

Thilo Beckmann