Search found 15 matches

by LTC
Mon Apr 10, 2006 8:19 pm
Forum: General Discussion
Topic: 90 Watt LED Driver - Need a bit of help here :)
Replies: 57
Views: 10839

I am not really interested in throwing caution to the wind here.... this circuit is designed to run 24/7 with a MTBF of 100,000 hours+. When you say that I would be ejecting precaution for dollars, what exactly do you mean? Above all else, this circuit should have no safety concerns, even in fail mo...
by LTC
Mon Apr 10, 2006 5:30 pm
Forum: General Discussion
Topic: 90 Watt LED Driver - Need a bit of help here :)
Replies: 57
Views: 10839

I really do not want to convert a 12v ATX power supply into a 48v+ supply, go the PWM route or use just resistors. I have seen one circuit that is getting close to what I need. But I really want to adhere to KISS on this one. Some concepts, while great, are taking things a bit too far. I want to kee...
by LTC
Mon Apr 10, 2006 5:25 pm
Forum: General Discussion
Topic: 90 Watt LED Driver - Need a bit of help here :)
Replies: 57
Views: 10839

Re: What a great place

First, it is a pleasure to meet so many people that care about LEDs and supplying current. Felt very alone in my experiments... I keep hearing about the K2 LEDs from some of you guys?? Has anyone actually gotten hold of a white 140 lumen version?? I have been on backorder for MONTHS.... They are no...
by LTC
Wed Apr 05, 2006 2:06 pm
Forum: General Discussion
Topic: 90 Watt LED Driver - Need a bit of help here :)
Replies: 57
Views: 10839

Um - guys... no need to fight here. I do not think that PWM is not the best approach for this application although it has many other very valid uses. I have read up substantially on the circuit design for this circuit and it seems to me that the best approach is to go with a boost type circuit. The ...
by LTC
Fri Mar 31, 2006 5:53 am
Forum: General Discussion
Topic: 90 Watt LED Driver - Need a bit of help here :)
Replies: 57
Views: 10839

Can the PC power supply provide 10.8A on +12V lines? Probably not. It absolutely can. I intend to use a 300W Switching ATX PC Power Supply. It is rated for about 20A on the +12 Line. The ATX specs drive power from 11.4-12.6v. My assumption about the LEDs is that they have a voltage/current band. Wh...
by LTC
Thu Mar 30, 2006 9:17 pm
Forum: General Discussion
Topic: 90 Watt LED Driver - Need a bit of help here :)
Replies: 57
Views: 10839

Almost there...

Lots of mixed ideas and experience here. My design criteria is this: safety, power use, cost, simplicity. Here is what I am hearing. Transistor controlled or resistor controlled. A transistor and resistor build seems awkward and you lose a great deal of power with this method? What role does the tra...
by LTC
Tue Mar 28, 2006 10:18 am
Forum: General Discussion
Topic: 90 Watt LED Driver - Need a bit of help here :)
Replies: 57
Views: 10839

Re: 90 Watt LED Driver - Need a bit of help here :)

Here is the data sheet for the K2 http://www.luxeon.com/pdfs/DS51.pdf Specifically look at page 14 - voltage depends on the temperature as stephan astutely pointed out. This is the kicker. I need to design a circuit that minimizes power use but maintains the KISS principle and does not cost an arm a...
by LTC
Tue Mar 28, 2006 10:12 am
Forum: General Discussion
Topic: 90 Watt LED Driver - Need a bit of help here :)
Replies: 57
Views: 10839

Re: 90 Watt LED Driver - Need a bit of help here :)

I think my biggest problem is understanding what happens to the LEDs due to themal effects. If I put 3 in series, say they each draw 3.5v ideally. That is 10.5v @ say 700 mA. That is easy enough. Make sure you have the correct regulated 12v coming in, the proper ohm resistor and the correct wattage ...
by LTC
Mon Mar 27, 2006 5:59 pm
Forum: General Discussion
Topic: 90 Watt LED Driver - Need a bit of help here :)
Replies: 57
Views: 10839

Re: 90 Watt LED Driver - Need a bit of help here :)

Oops you are correct. I meant to quote Externet. The only problem is that I cannot easily put more than 20A across the 3.5v line in a normal power supply. If I am to drive 70+ watts, this seems like a bad idea. I could drive @ 5v and use a resistor to minimize the current but that also seems to be a...
by LTC
Mon Mar 27, 2006 2:31 pm
Forum: General Discussion
Topic: 90 Watt LED Driver - Need a bit of help here :)
Replies: 57
Views: 10839

Re: 90 Watt LED Driver - Need a bit of help here :)

Originally posted by Chris Smith: 3 x 3.75 V = 11.25 V. Either trick or adjust the voltage in the power supply to come down to ~11.25 or drop the excess with a silicon diode. No resistors. Is that not a really BAD idea? What happens when the LEDs heat up? Their resistance changes, and they start pu...
by LTC
Mon Mar 27, 2006 1:43 pm
Forum: General Discussion
Topic: 90 Watt LED Driver - Need a bit of help here :)
Replies: 57
Views: 10839

Re: 90 Watt LED Driver - Need a bit of help here :)

Originally posted by KamPutty: Whats your plan for the heat build up? I'm playing with smaller LED's (3.[email protected] / 42 Lumens), not the 1000mA you have, and that single LED builds up alot of heat. ~Kam (^8* 18 1" by 1" heatsinks and a fan. No doubt this thing will get warm but should give off less h...
by LTC
Mon Mar 27, 2006 7:53 am
Forum: General Discussion
Topic: 90 Watt LED Driver - Need a bit of help here :)
Replies: 57
Views: 10839

Re: 90 Watt LED Driver - Need a bit of help here :)

As to ensuring the power supply is up to the task. Each LED = 3.75w (3.75 V @ 1000 mA) Assume I have 6 rows of 3 leds, each serial row takes up approx 12v + 1 mA. Since there are 6 rows, each taking up 1mA @ 12v, the total power use is 6 amps @ 12v, not 18 amps @ 12v. (6*12=72 watts) (18*12=216 watt...
by LTC
Mon Mar 27, 2006 7:47 am
Forum: General Discussion
Topic: 90 Watt LED Driver - Need a bit of help here :)
Replies: 57
Views: 10839

Re: 90 Watt LED Driver - Need a bit of help here :)

1000 mA is the normal and maximum rating. They can be run at 700 mA - but less light output (of course). Your transformer example sounds like a good idea but what happens when the AC input current were to change? Not likely but certainly possible if it spiked. What happens to the current output when...
by LTC
Mon Mar 27, 2006 3:02 am
Forum: General Discussion
Topic: 90 Watt LED Driver - Need a bit of help here :)
Replies: 57
Views: 10839

Re: 90 Watt LED Driver - Need a bit of help here :)

The LED heatsinks are not electrically neutral. Makes heatsinking a pain. Why go 48v or 120v ac? Why not just use a 12v source? 6 rows of 3 = 18 with very little power loss. 9 Watts.... 87.5 % efficiency atm, not counting ac->dc losses. I agree though, most leds fail open. The gold wires act as fuse...
by LTC
Sun Mar 26, 2006 3:13 am
Forum: General Discussion
Topic: 90 Watt LED Driver - Need a bit of help here :)
Replies: 57
Views: 10839

90 Watt LED Driver - Need a bit of help here :)

I know a thing or two about electronics, but when it comes to the really complex stuff, it seems like a good idea to get the assistance of those in the know. Ok so maybe this is not THAT complicated but it is beyond me right now. You guys really know your stuff. Can somebody who knows more about thi...