Convert Laptop Adapter(19v) to LED Driver?

[martyparish]

I have a Chinese 100w LED. DC Forward Voltage(VF):30~34Vdc ; DC Forward Current(IF):2400MA

I want to try to see if it's possible to modify a 19v adapter to run it. I have been reading about modifying smps to raise their voltage and have actually been successful(miraculously lol) so far at getting it from 19v to 25v.

The power supply:
HP 380467-003
INPUT: 100-240V 50-60Hz 1.6A
OUTPUT: 18.5V 3.5A 65W

I know I could buy a proper driver but I want to learn and have some fun Also the drivers are a bit costly. If this could work, it would be sweeeet!!

What I've done:

After researching for a long time I finally believe I figured out the feedback circuit and by lowering the resistor value gradually I got the voltage up to 25v but when I try to go farther it shuts down.

I'm assuming some other over voltage protection but I can't figure it out so far...

First, do you guys think this is possible? I realize it's only 65watt adapter but I'd be fine driving the LED at that power and fairly sure it will operate. Plus, if it works, I'll just get higher rated adapter for next version!

Also, the second big question:

How could I integrate constant current into this?


Pics attached and many thanks fellas!

[stj]

Re: Convert Laptop Adapter(19v) to LED Driver?

answer is no,
you need regulated current, not regulated voltage.

[martyparish]

Re: Convert Laptop Adapter(19v) to LED Driver?

I'm aware that LEDs want constant current. Maybe you could give a little more info on why this cannot be converted to sense current? Like I said, I'd like to actually learn something! Thanks for the response.

[stj]

Re: Convert Laptop Adapter(19v) to LED Driver?

it uses a chip designed most likely for constant voltage, and the transformer secondary is wound for 19v.

get a datasheet for that chip, but i wouldnt try to get double the voltage from it anyway.

[martyparish]

Re: Convert Laptop Adapter(19v) to LED Driver?

Thanks stj! You're talking about the pwm chip right?

It is labeled HP3D6 and I cannot find datasheet on it but I think it's same as NCP1203. (I've compared typical application to this board and pins are same)

https://cdn.badcaps-static.com/pdfs/...ff378b36a8.pdf

but i wouldn't try to get double the voltage from it anyway

I figured I may be trying to push it too high but I'd like to see how far it will go. There are some nice Vero leds that would run at around 26v I think.

[mariushm]

Re: Convert Laptop Adapter(19v) to LED Driver?

The power supply uses a controller designed to control voltage, not current.
By playing with resistors on the voltage reference, you can adjust voltage a bit but up to a certain point due to other factors like the transformer used and the secondary capacitors (which are most likely rated for maximum 25v).

For leds you need to control the current.
The led will probably turn on and be somewhat bright even at 19v and the low voltage will most likely prevent the leds from going beserk and use so much current as to blow up.
But, as you get close to the rated voltage, you need to control the current carefully.

You need a proper led driver, and there's boost/step up drivers or buck/step down drivers. Since you need 34-36v but your voltage is 19v, you need a step up driver.
The efficiency of such drivers isn't that great, it's probably around 85% so you have to keep in mind that... your led will consume 35v x 2.4a = 84w so your power supply will need to be able to provide about 84w x 100/85 = ~ 97w - your 65w laptop adaptor is not powerful enough to power up that led.

If you change that to a 24v psu or a computer psu (where you have 30-60A at 12v), then you don't have problems anymore.

See here led driver chips, choose step up and make sure the chip can boost that much current and then check datasheets to see circuit examples and figure out what extra components you'd need :

http://www.newark.com/led-drivers

There's ready made led drivers here... pick ones that can do the voltage you want and the current, though i guess those will be kind of expensive. Not even sure they sell such high wattage drivers: http://www.newark.com/dc-dc-converters-led-driver

Also.. a warning... a 100w led will need serious cooling, picture a large heatsink (or a cpu cooler with heatpipes) and fan blowing air on the heatsink to keep the temperature down.

[martyparish]

Re: Convert Laptop Adapter(19v) to LED Driver?

Thanks mariushm for the in depth reply. I guess I'll have to stop kicking this dead horse lol. I did learn something though and had a bit of fun.

Building(or buying) boost drivers may be a plan because I will most likely want to run multiple LEDs. I don't like the idea of buying an ac/dc driver for each LED, which is what I see many people doing.

Also, I'll NOT be using these cheapo LEDs in the end, these are just to experiment and get things straight before I buy Cree or Bridgelux @ ~$30 - $40 each. I may decide to go down on the power of each LED as well. 100w are a bit extreme for what I need really.

I have the cooling covered. What I really need to be careful of is looking at these things... even the 10w version will mess your eyes up!



Anyway thanks again fellows! Maybe I'll pop back in with some boost driver questions later.


Peace!

[CapLeaker]

Re: Convert Laptop Adapter(19v) to LED Driver?

as long as you are UNDER the voltage rating of the LED, there is no CC needed, but it is up to you to ensure it's not going over the voltage rating of the bulb. So will it light with that laptop charger? Yes. Just not to its full potential. Any voltage swings and the bulb goes dimmer or brighter. Why do I need CC then? for an even light regardless of voltage swings and never to go over the voltage what the bulb is rated for.
What happens if I put more voltage in an LED, then what it is rated for? It will consume more current than it should, the LED's go brighter than they should, then pop at some point.

LEDs don't draw more current than they aren't able to handle UNDER the voltage rating, because they haven't reached rated voltage yet!
I can take a 3.3V LED, give it 3.oV and hook it up to a 50V,10A adjustable CV power supply. No problem. Or I can use a 10A CC supply and adjust it for 15ma and get 3V for the LED.

[martyparish]

Re: Convert Laptop Adapter(19v) to LED Driver?

Thanks CapsLeaker. It won't light at 19v and barely starts to light at 25v.

LEDs don't draw more current than they aren't able to handle UNDER the voltage rating, because they haven't reached rated voltage yet!

That's why I was hoping to squeeze close to 30v from this unit. I figured the led would be fine. I would be perfectly happy running the LED way below MAX ratings for a few reasons(less cooling required, longer led life).

Let me switch gears for a sec. What do you guys think about running multiple boost circuits off of one single 400-600 watt 24v PSU?

[Th3_uN1Qu3]

Re: Convert Laptop Adapter(19v) to LED Driver?

I would rather modify the 24v PSU for 30v and build a constant current driver for the LED.

[martyparish]

Re: Convert Laptop Adapter(19v) to LED Driver?

Hey Th3_uN1Qu3 thanks for the reply! I've read your other threads where you modify PSU voltages. It gave me some inspiration! Very good stuff.

Do you have any specific PSU that you would use? I'd love to hear any ideas you may have!

I'll keep digging and reading for the time being.

Thanks again!

[Th3_uN1Qu3]

Re: Convert Laptop Adapter(19v) to LED Driver?

You can choose any 24V PSU with enough output power for your application. Modifying the output voltage is the same for all of them.

[mariushm]

Re: Convert Laptop Adapter(19v) to LED Driver?

Also, I'll NOT be using these cheapo LEDs in the end, these are just to experiment and get things straight before I buy Cree or Bridgelux @ ~$30 - $40 each. I may decide to go down on the power of each LED as well. 100w are a bit extreme for what I need really.

Peace!

That's a good idea. Those eBay leds aren't reliable, they're often not really 100w but more like 70-85w, they're lousy at color reproduction (low CRI) and lousy color temperature (blueish tints or something like that).
In addition to that, you'd really have a hard time keeping them cooled, the heatsink would be expensive, too much concentrated in one small point.

I've tested a led that costs about 10$ on Farnell (Newark, site I linked to above) with high CRI and good color temperature: http://uk.farnell.com/webapp/wcs/sto...&storeId=10172

It's rated for 21v @ 0.5A (so about 11w) and the brightness is pretty much equivalent to 90-120w incandescent lightbulb but a very nice white. It starts from about 16v but current limiting is needed from about 19v.

With a 24v power supply, a led like this is super easy to drive, the led driver can simply be 2-3 of these chips ( http://uk.farnell.com/on-semiconduct...2-3/dp/2382343 ) in parallel (because each can do about 0.35A max, so you need 2 to get 0.5A or more), plus 2 resistors to allow you to adjust the current. Easy to solder on a small prototyping board or small pcb.

So it's super easy to put a bunch of leds and the 2-3$ driver for each on an aluminum/copper strip which would also act as heatsink.

[martyparish]

Re: Convert Laptop Adapter(19v) to LED Driver?

Thanks mariushm. You don't trust the eBay parts to be within specs??? LOL! Me neither. They are decent to toy with and if I blow one no big deal.

I like the LEDs you linked to as well. ($7 on digikey) I'll to compare those side by side with the Vero(also bridgelux) and Cree of similar specs. Thanks for the link!

These Lumileds by Philips also look promising! I saw one that put out 141 lm/W! That's pretty high! Even the best Cree were lower than that.

http://www.philipslumileds.com/

And thank you for the ideas on the drivers!! I'm all for finding LEDs that will run on 24v or less!

Now to figure out what to do with this 19v laptop adapter that I hacked

[stj]

Re: Convert Laptop Adapter(19v) to LED Driver?

i notice the farnell leds have optional bases & lenses etc - nice.

[mariushm]

Re: Convert Laptop Adapter(19v) to LED Driver?

Before you do anything, you should read on CRI and color temperature.

Cheaper LEDs (and the ones with high lumens per watt in most cases but not always) have low CRI which affects how your eyes perceive colors when light shines on things.

Think of it like having a cheap fluorescent bulb (let's say CRI 60-70) in a bathroom with blue or green tiles.. the blueish tint of the fluorescent bulb would make your white skin look like the one on cadavers due to reflections from the tiles in the bathroom and the light spectrum the bulb makes.

It's possible the $7 version you mention is only CRI 70, the led I linked to is CRI 80 which is a bit above a quality fluorescent lightbulb. There are versions with CRI 90 or better but they're more expensive. For floodlights, where you don't really care about color reproduction, you just want things lit up, low CRI is not a problem...

On the other hand, if you want for example to make some lightning jig for your desk to record videos or if you do some photoshop work on your monitor, you don't want the lightning in the room to affect how you perceive the colors around you.

Color temperature also matters.. my led is 4000k which is a bit of a colder white but was cheaper than 5000k. 5000k is desired for photography and video recording, it's neutral white, cameras can do color and gamma correction internally easily with that temperature... cheap leds are usually 2400-2900K which isn't that great.

[martyparish]

Re: Convert Laptop Adapter(19v) to LED Driver?

I have done quite a bit of reading on the subject but I can say it's not 100% clear but I'm getting better. Thanks for the explanation!

I should have mentioned that my LED projects will involve reef lighting and plant growth generally(but I'm certainly thinking about it for my area lighting!).

Even so, color and cri matter to me still!

The $7 LED I linked to is the exact one you linked. I guess it's just the price difference between digikey and farnell.

As far as the High lm/watt ones(the lumileds, I went and looked again and they are generally all 80cri! I'm seriously considering ordering a strip.

Check them out here if you are interested

[martyparish]

Re: Convert Laptop Adapter(19v) to LED Driver?

I love talking LED But to steer this back to the original purpose, here's what I will do with the 19v adapter that I started with.

I'm just going to tune the volts to drive two 10w LEDs in series. (9-12vf)

@mariushm I'll take your advise and put a CC regulator in front of the series.

At least I'll have done something with this HP adapter and learned along the way

Thanks!