I’ve built a couple of them before. Mainly used as electronic variable current loads for power supplies. It actually would not be too difficult to build a driver using the technique… but ’7135 chips are cheap and easy to use.
With the copper mounted xml2 and xpg2 leds nowadays it makes more and more sense to direct drive them off a single Li-ion, most batteries are not capable of delivering the 8+ amps to blow the leds, even a 18650 IMR has enough voltage sag to keep the current through an xml2 low enough not to blow it , and with direct drive you get the maximum output possible for the set-up.
How does these FET drivers work like the east92 and the “5A v10” driver? I guess they work like this, but the FETs used have a high onresistance to limit the current.
I am not sure what these spikes cause with a led but I guess if they degrade a bit faster it plays no big role for a flashlight as the total lighting time is not so big.
Has anyone found a specification for peak current on cree LEDs?
In the nichia 219 datasheet are 2A stated…
Could someone with faster Internet watch the videos linked on the end of this document in point 2…
http://www.cree.com/~/media/Files/Cree/LED%20Components%20and%20Modules/XLamp/XLamp%20Application%20Notes/XLamp_Elec_Overstress.pdf
Edit: I found a nice application note
http://www.cree.com/~/media/Files/Cree/LED%20Components%20and%20Modules/XLamp/XLamp%20Application%20Notes/XLampPulsedCurrent.pdf
Luminous efficiency decreases with the pulsing and chromaticity shift compared to a constant current and of course less lifetime…
Are you talking about that supposed V10+ driver from FT? That doesn’t come close to 5 amps from my testing, and FT reviews say the same thing.
From that last document:
I found what I was looking for in the second document too:
*Based on the 1-KHz pulse testing we have reviewed in this application note, cree suggests the following guidelines for pulsed current operations:
- For duty cycles between 51-100, do not exceed 100 of the maximum rated current;
- For duty cycles between 10-50, do not exceed more than 200 of the maximum rated current; 3. For duty cycles less than 10, do not exceed more than 300 of the maximum rated current.
In addition to degradation in light output, other properties that may be affected by high-current operation over the long term are color-point stability, reverse-leakage current and forward voltage. cree recommends that customers perform their own long-term testing to ensure the reliability of their design*
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We know that we all like to overdrive leds, but this doesn’t look so bad. I don’t see a problem in direct drive pulses from a Single battery and a XML
Or, just to throw the idea out there. A 7135 based driver that has say 4 7135 chips on it for up to 1.4 amps of current regulation, and then a mosfet taking up the rest of the space (so as to supply a direct drive option).