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Ultra Short, Ultra Fast LED Flash

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ogden:

--- Quote from: JAndrew on March 09, 2019, 11:09:27 pm ---I'm interested mainly in just the charge and trigger.

--- End quote ---

Only thing you need from that flash is charge stored in the capacitor. Xenon flash trigger is no use anyway, LED needs high voltage transistor driven from high power gate driver (refer to 4ns LED flash circuit posted here). You may even leave that flash thing unmodified and operable if needed, just tap capacitor for your LED project. COB's you mention looks good as well (for starters), hopefully their bonding wires will not explode when overdriven. Flash voltage is specified 310V, so you need ~4 COB LED's in series for 200% power, then you "improve" it further until it explodes.

Be careful. Hopefully you know how to handle high voltages, 1000uF@300V (~50 joules of energy) is deadly.


--- Quote from: Marco on March 09, 2019, 11:23:36 pm ---Just drive them with a MOSFET, the capacitive discharge method is for xenon tubes ... it's a bit silly for a LED.

--- End quote ---

Right. LED shall be connected to capacitor and after 500ns transistor shall be switched off. You do not leave LED after trigger connected to cap forever, such way it is impossible to get short pulses.

Marco:
That's why the 12V COBs are nice, if you use the 70W version which Big Clive reviewed then 36V should get you roundabout 20x the current. Nice low voltage.

You might need one driver+MOSFET per COB, but the voltage stay safe.

JAndrew:
I wanna make sure I'm understanding the idea.

We use the charging circuit, but the rest of the circuit isn't needed since we're not driving a Xenon flash. Instead we tap in a MOSFET rated for medium voltage, and trigger the MOSFET (in this case we have a logic level MOSFET driving the larger MOSFET) to flash the LEDs.


--- Quote ---(refer to 4ns LED flash circuit posted here
--- End quote ---

Which one was this one exactly?


--- Quote ---Hopefully you know how to handle high voltages, 1000uF@300V (~50 joules of energy) is deadly.
--- End quote ---

I was hoping to stay away from high energy sources. It looks like it's going to be unavoidable. I'll be brushing up on the safety aspects of this project before embarking on it.

Marco:
You need high energy, but you don't need high voltage.

ogden:

--- Quote from: JAndrew on March 10, 2019, 12:00:59 am ---I wanna make sure I'm understanding the idea.

We use the charging circuit, but the rest of the circuit isn't needed since we're not driving a Xenon flash. Instead we tap in a MOSFET rated for medium voltage, and trigger the MOSFET (in this case we have a logic level MOSFET driving the larger MOSFET) to flash the LEDs.

--- End quote ---

You use MOSFET driver IC which have high current push-pull drive capability. Single mosfet driving other mosfet's gate will not be fast enough. You need both - *fast* turn-on and turn-off of the main MOSFET. Sorry, I did mean 4us flash, not 4ns. There's circuit in this post:

https://www.eevblog.com/forum/beginners/4-microsecond-high-power-pulses-through-led/msg1417075/#msg1417075


--- Quote ---I was hoping to stay away from high energy sources. It looks like it's going to be unavoidable.

--- End quote ---

High voltage is avoidable, you just need bigger wires, capacitors and transistors because currents are higher :D As Marco suggested - to avoid high voltage you may use 12V COB's in parallel, then you mau get away with safe <50VDC voltage. Which way to go - up to you. We (forum members) are not your parents.

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