Flashlights

These are fun!

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Triple 'LVC buffer drives the power transistor at 5 or 6 nanoseconds risetime, not bad at all.

Design is very hackable; by changing around a couple of resistors, it makes a portable bench supply!

Tim

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Tim Williams
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Your design Tim? Otherwise where are they available?

Clifford Heath.

Reply to
Clifford Heath

so it's promotional

why so much electronics in a flashlight?

Reply to
tabbypurr

Looks bright.

Some of those tiny CMOS parts are insane.

NL37WZ16US, all three sections in parallel:

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and I've seen much faster.

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John Larkin         Highland Technology, Inc 
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John Larkin

That's the lowest setting. :^)

They're capable of 10W, though the 18650 cells I have aren't capable of that much, they start to brown out (the circuit has an undervoltage limit so it doesn't collapse).

Needless to say, full brightness does not photograph very well...

Yup. These gates have a pretty good load on them, actually: the Vgs waveform is about 20ns. And the power transistor is sharpening up the rest.

Tim

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Reply to
Tim Williams

Buy now and get 5% off! :-P

It's a demonstration -- discrete (transistors, comparators, op-amps and a gate driver) yet full featured. Boost converter, average current mode control, 2% regulated output voltage/current, adjustable, overvoltage (output) limit, undervoltage (input) limit, overtemp limit.

You know, everything you get inside a teeny $1 IC, for the price of $20 in parts and a whole PCB. :-)

Tim

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Tim Williams

Yes. Nowhere yet, haven't decided if I'll just do it on a one-off basis, or make a kit of it. I should see what Tindie is like for these sorts of things...

In any case, do send me an e-mail if you're interested. :)

Tim

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Reply to
Tim Williams

Is that the LED current rise time or the rise time of the photo current? (a modulation input somewhere?)

George H.

Reply to
George Herold

Boost converter, filtered output. Risetime is of the converter switching.

Modulation isn't very fast, on account of the converter + controller being a big filter, ~kHz BW.

It would be less efficient (and much more EMIey :) ) if the LEDs were right across the boost inductor (and also slightly harder to regulate current), due to the RMS AC current in the LEDs' ESR. The blue spectrum would have about that rise time then, though.

But you could also assemble the design that way, if you so desired.

Tim

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Seven Transistor Labs, LLC 
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Reply to
Tim Williams

I'm not seeing the point of it.

NT

Reply to
tabbypurr

Those tiny buffers are so cheap that you can put two or three in parallel, at three gates per chip. More drive, less wirebond inductance. Run them at abs max Vcc, of course.

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John Larkin         Highland Technology, Inc 

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John Larkin

Even three in parallel, Rds about 5 ohms, right? It'd be nice to be 10 to 20x lower.

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Reply to
Winfield Hill

Sounds about right.

Sure, but that gets more complicated. And expensive. Inductance gets to be an issue out there.

An alternative is to use multiple smaller fets in parallel, each with a couple of private tiny-logic gate drivers.

That spreads out the L di/dt's and the thermals.

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John Larkin         Highland Technology, Inc 
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Reply to
John Larkin

Damn. Use enough heatsink there, Butch?

How warm do the LEDs get, anyway?

Kewl. What voltages/current limits?

Add a USB charging port and I'm in.

Oh, uh, I should probably ask- what's the projected retail price point?

Mark L. Fergerson

Reply to
alien8752

I measured up to 70C in a somewhat enclosed space -- in thermal limit.

Out in the open, it does about 60C at 5W. The circuit will do 10W, but not all cells will. :)

The cell is removable (or I guess you could shove some wires in and charge it that way). Not that 18650 chargers are all that common.

Input voltage limit 3V (less and output current falls sharply), output voltage limit 12V (just with a zener to the feedback node), output current

1A, input current, absolute maximum somewhere around 5A I think.

I have to look up how much they charge for kitting + fullfillment on this sort of thing. It should be a nice kit for most learners, and with all the control and sense signals accessible, it can be hacked into lots of things, limited only by your imagination.

Tim

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Tim Williams

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