Electronics > Projects, Designs, and Technical Stuff
Ultra Short, Ultra Fast LED Flash
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JAndrew:

--- Quote from: schmitt trigger on March 07, 2019, 04:19:00 pm ---
--- Quote from: JAndrew on March 05, 2019, 11:06:50 pm ---

Jay

--- End quote ---

Doc Edgerton himself would be proud of this photo

--- End quote ---


Thanks man, I’ve got a collection of similar photos, this is probably the one I am most proud of.


Sent from my iPhone using Tapatalk
T3sl4co1l:
The biggest problem is getting enough peak power.  LEDs aren't good very far beyond ratings, unfortunately.  (The efficiency tanks, and then eventually you get accelerated damage, and outright failure.)

Tim
Giaime:

--- Quote from: ajb on March 06, 2019, 07:31:19 pm ---Many switching constant current LED drivers support PWM dimming by using a transistor to short the LED(s), so you could do the reverse here.  Establish your target current in the inductor, then open the switch across the LEDs for your desired duration, then close it again.  If the pulse is long enough and the response of the switching converter is fast enough the converter will pick up the load to maintain the LED current, otherwise you can just use a big enough inductor to sustain your required pulse.

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Been there, done that. This is the best way. Use Ti parts like LM3409 or TPS92641, TPS92515, etc, all support shunt PWM dimming. You can get 300-500ns pulses like that if you control the circuit inductance carefully.
ogden:

--- Quote from: Giaime on March 08, 2019, 08:24:06 am ---
--- Quote from: ajb on March 06, 2019, 07:31:19 pm ---Many switching constant current LED drivers support PWM dimming by using a transistor to short the LED(s), so you could do the reverse here.  Establish your target current in the inductor, then open the switch across the LEDs for your desired duration, then close it again.  If the pulse is long enough and the response of the switching converter is fast enough the converter will pick up the load to maintain the LED current, otherwise you can just use a big enough inductor to sustain your required pulse.

--- End quote ---

Been there, done that. This is the best way. Use Ti parts like LM3409 or TPS92641, TPS92515, etc, all support shunt PWM dimming. You can get 300-500ns pulses like that if you control the circuit inductance carefully.

--- End quote ---

Why, why do you people suggest such  :bullshit: ?

First one, LM3409. Datasheet states that buck regulator frequency above 1MHz is hard to achieve. This means that one buck regulator pulse alone is longer than required, not to mention that first pulse most likely will not reach nominal current. Following waveform from LM3409 DS clearly shows problem why buck regulator and inductor-based approach as such is not the best choice (to say it politely) for this application:

StillTrying:

--- Quote from: ogden on March 08, 2019, 09:45:11 am ---buck regulator and inductor-based approach as such is not the best choice (to say it politely) for this application:
--- End quote ---

Yes, I think a charged cap is the only way the energy can be stored for many minutes while waiting for the trigger, storing it in an inductor adds all kinds of timing problems.
But the biggest problem is still getting the LED light up to 10s of kW for very short exposures.

This ~5.7kW for 4us one mentioned above is about the best I've seen anywhere on the web.
https://www.eevblog.com/forum/beginners/4-microsecond-high-power-pulses-through-led/
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