Thanks for the quick reply, indeed I was bit misguided by the datasheet.
With MC34063, what would be the disadvantages of the "Feedback Control" design as shown here ?
http://www.jiggerjuice.info/electronics/projects/power/LED-drivers.html
Is there any risk of overcurrent condition when the device starts ?
No more than usual, I suppose.
It simply outputs pulses while the input is below threshold, and stops when above. By setting feedback to a voltage drop across a series resistor, output current is controlled. The amp is simply to reduce the voltage drop on the resistor.
I have some MAX5033 which both includes thermal and short-circuit protection, so I can use one of them with feedback loop if needed. I do not really want to lose an eye.
https://datasheets.maximintegrated.com/en/ds/MAX5033.pdf
Hmm, the current limit may be right, such that you can just run it full bore into the LED. It does claim a "hiccup" mode which would be undesirable, but it doesn't say how it works. (Often, FB voltage is sensed, and when it's well below the nominal threshold, the oscillator frequency is stepped back, or the soft-start circuit is triggered, etc. Neither of those possibilities is shown on the block diagram, however.) It would need to be tested. Otherwise, sure, with the current sense amp, that method will work too.
FYI, I generally avoid Maxim parts, as they tend to be special purpose and suffer from poor availability. For one-offs, meh, if it works it works.
What would be the advantages of a true current mode controller compared to step-down DC/DC controller with feedback loop ? Would
https://datasheets.maximintegrated.com/en/ds/MAX1953-MAX1957.pdf work for this application ?
A whole-ass controller seems overkill for a 1W LED, but yeah, that'll work. Same thing, not sure if the limiting behavior will be well enough behaved to use directly or if it needs a different feedback path. Neat part here is, by sensing inductor current via Rds(on), you can trim that with a series drain resistor to reasonable accuracy (note Rds(on) varies widely with manufacture and temperature).
If nothing else, you can use voltage regulators like these, in the usual way, setting the voltage just a bit over what the LED needs. Simply use a series resistor to set LED current. The efficiency is somewhat worse, but still a whole heck of a lot better than with no switching reg at all!
Consider shopping for purpose-made devices. There are oodles of LED drivers out there, should be something to do exactly what you want, just add inductor and capacitors, maybe a resistor or two. (I don't know any offhand; the last few LED drivers I used were boost type, for series-connected display backlights.)
Final question: is that design https://www.instructables.com/Poormans-Buck/ reliable ?
The schematic is a... video? It's cropped, I can't even see the whole thing? WTF?
Instructables is, in general, a poor resource...
Tim