Recent content by space

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    Constant current driver

    SirJMD: As I said you really should start to simulate this circut. The output impedance of your transformer will very likely be so high that the inductor is not needed. (Your 15VAC transformer is also an inductor. A rather large one.) space
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    Constant current driver

    This is for SirJMD: I think you should start to simulate this circut. I don't belive this can be called constant current. LED's will go to 0 current on each cycle. What frequency is the supply? The inductor could probably be dropped. space
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    Grapchite PCB?!

    I'm quite aware of your work from reading your most often very interesting posts on this forum. As you are running your LED way over spec, the higher energy density of course benefits a lot more from a highly effective heat spreader (you are using solid copper ones right?). But for the...
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    Grapchite PCB?!

    When I say "...normally used..." I already mean MCPCB, or FR4 with a lot of small vias as suggested with the Rebel. space
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    Grapchite PCB?!

    I very aware of this, but close to the LED die here, for me actually means LED die to substrate/solder point which is set with the design of the LED, which we can't do anything about. Thermal resistance is stated as "as low as 9C/W" for XP-e. What is the thermal resistance for a "normal" MCPCB...
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    Grapchite PCB?!

    Sorry about that. Not my intention to kill your enthusiasm. Spending time on learning up on new exiting stuff, even if it doesn't end up as "use full", is what I do must of my spare time, and I love it. It is very easy and often occurring when starting exploring new fields, to get sidetracked...
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    Grapchite PCB?!

    Going for a PCB with 100x better heattransfer that what is normaly used, will not gain you anything. The clue is getting good heattransfer from the heatsink to ambient (the air). This is where you can improove efficiency. If efficiency is really vital, then running many LED's at lower currents...
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    How to drive 20 CREE XP-E in series parallel

    What is meant by flashing? For how long will it be on? And how often? Will the leds be run when the battery is charging (in a running car for instance)? (Means that ~12v will get up to 14.4v.) or maby mostly when the battery is charging? Is it ok that the output drops off abit when the voltage...
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    How to drive 20 CREE XP-E in series parallel

    You need to specify more about your application: More info on the power supply (what kind, max/min voltage) How hard are you planning on driving the LED's? / Do you have good heat sinking in the application? Do you need to have constant output? (Constant current to LED's?) Do you have good heat...
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    SSC P7 dome apperance

    I have also noted that some of my P7's have clouded domes. space
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    The most efficient use of an LED?

    The fantasic White LED lumen testing-thread by jtr1962, shows that almost all LED he tested have highest efficacy when driven with a voltage equal to or just above the band gap energy for the LED. For most white LED's, in which the LED emits 450nm wavelength blue light, it translates to ~2.75V...
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    Heat Question

    One of the best ways to increase efficacy, is to use more LED's (more die area) at lower current/power. More LED's mean lower Vf = less heat and lower die temp, both lead to higher efficacy. It will of course cost you. space
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    Is the XP-E the brightest red-orange LED @350mA?

    The lumen scale is based on the human eyes sensitivity, so the reason for the red-orange having 67 lm as opposed to reds 52 lm, is mostly due to the eyes different sensitivity at those wavelength. So if both were 60 lm, they would appear equally bright. space
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    SSC P7 backordering!?

    Yes the lettering is related to luminous flux, color and electrical properties (voltage required at default settings). All of this you can read about in the P7 series binning & labelling datasheet. The letters you are referring to is described on page 2, section 3. Code Labeling. space
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    Playing a little with an SST-50 ...

    And the Vf wasn't measured at the LED was it? At 5A there will be a fairly substantian drop in the wires. space
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