Electronics > Projects, Designs, and Technical Stuff
Ultra Short, Ultra Fast LED Flash
mzzj:
--- Quote from: ogden on March 09, 2019, 09:14:24 pm ---
--- Quote from: JAndrew on March 09, 2019, 08:59:22 pm ---Pretty inexpensive for 10,000LM, but if I drive these by 1000% and get 10 of them. Then I could match the 1mil Lum.
10K lm? - Scam. With such specs he can put OSRAM out of business, yet they are doing well :) You may indeed user those to start with, but do not expect to get even close to specified light output. Not to mention CRI
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10k Lm out of 100W COB is hardly any sort of state-of-the art nowadays so its certainly possible even for low cost chinese COB.
Probably the chinese are bit "optimistic" and you get only 8kLm and lifetime is certainly a mystery vs. more expensive brand name product.
Siwastaja:
--- Quote from: ogden on March 11, 2019, 08:50:53 am ---
--- Quote from: Giaime on March 11, 2019, 08:07:11 am ---Here you can see a measurement on one of the systems I work with.
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One scope screen is worth thousand words :) Thanx! I am really surprised that it works so well. Until now regarded shunt PWM as snake oil, especially when saw na'ive simulated waveforms in the TI datasheet.
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Shunt switching, driven from a constant current supply, is widely used in 3D Time-of-flight designs, with pulses down to around 10ns. I designed mine using a voltage source and series resistor instead, encouraged by our chip supplier's reference design with such a simple topology, but OTOH I'm only modulating at 20MHz (hence, 25 ns pulses with 25ns offtime). Works well enough for us, although we do see a drop in differential "payload" signal amplitude at 20MHz, but I'm almost certain this is limited by the LEDs, more than by the switching topology.
Zero999:
--- Quote from: mzzj on March 11, 2019, 11:27:43 am ---
--- Quote from: ogden on March 09, 2019, 09:14:24 pm ---
--- Quote from: JAndrew on March 09, 2019, 08:59:22 pm ---Pretty inexpensive for 10,000LM, but if I drive these by 1000% and get 10 of them. Then I could match the 1mil Lum.
10K lm? - Scam. With such specs he can put OSRAM out of business, yet they are doing well :) You may indeed user those to start with, but do not expect to get even close to specified light output. Not to mention CRI
--- End quote ---
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10k Lm out of 100W COB is hardly any sort of state-of-the art nowadays so its certainly possible even for low cost chinese COB.
Probably the chinese are bit "optimistic" and you get only 8kLm and lifetime is certainly a mystery vs. more expensive brand name product.
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Yes, the CMA3090 I tested is rated for 12k Lm at the maximum rated drive current of 3.6A. Over-driving does increase the intensity, but it's not linear, especially at higher currents, which result in diminishing returns. According to the results of my experiment, with an LED drive of 35A, the photodiode current was 5.35 times, that when the LED was driven at the rated current, which seems a reasonable and is way below the 120A which was destructive. You could have an array of 16 LEDs, each driven at 36A to give 1M Lm.
Marco:
--- Quote from: Siwastaja on March 11, 2019, 12:23:11 pm ---Shunt switching, driven from a constant current supply, is widely used in 3D Time-of-flight designs, with pulses down to around 10ns.
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With much lower pulse energy. Inductive energy storage has multiple problems as you try to scale it up in energy. Bandwidth, inductor cost and standby power consumption. Bandwidth isn't really the problem here, inductor cost and standby power consumption are nearly insurmountable problems. You can either have a couple bucks worth of electrolytics which can run on AA batteries, or you can have a couple 100 bucks worth of inductors which require a mains connection and active cooling.
Get back to this when we get room temperature superconductors.
David Hess:
--- Quote from: Marco on March 11, 2019, 02:08:24 pm ---With much lower pulse energy. Inductive energy storage has multiple problems as you try to scale it up in energy. Bandwidth, inductor cost and standby power consumption. Bandwidth isn't really the problem here, inductor cost and standby power consumption are nearly insurmountable problems. You can either have a couple bucks worth of electrolytics which can run on AA batteries, or you can have a couple 100 bucks worth of inductors which require a mains connection and active cooling.
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If a fixed pulse width is acceptable, then a charge line or for longer pulse widths, a lumped delay line made from inductors and capacitors can be used instead of an inductor.
The way to do it in this application though is a switched current source or switched voltage source and ballast resistor.
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