High efficiency multi mode analogue LED driver

royfellows

Active member
I do seem to have hit a nerve with you Roy, certainly NOT my intention. Regards low battery voltage, why do you think nearly ALL reasonable kit shuts the circuits down at about 3v? No need to drain to 2.7v, and doing so can further complicate charging if the charging circuit does not attempt to kickstart the protection board into waking up again. Surprisingly common! I have also seen some boards not kick in until below the 2.7v level, which again, is not ideal!
Also, there really is no capacity between 2.7 and 3v. I suppose you could argue you do not want to stop at any voltage with caving lamps, but then again I suppose that is what backups are for!
I forgot to add that the low voltage cutoff could be micro-controller considerations but most these days have quite a wide operating range with low voltage modes down to 1.8v and below.
Not sure what you are referring to with regard to 5A. Did I state something to advocate such a current?
Its OK mate

Yes, the devil is in the data sheets.
Some Li Ion cells have higher recommended cutt off, generally earlier ones. Protection boards bought off the shelf may have a cut off set to a "catch all", to match to a specific array of cells may require some tuning so as to get the max burn time out of the battery by setting cut off to the recommended. Or more importantly, these last dregs before manufacturer recommended cut off often supports a diminishing output, we call the "slow death". Note "manufacturer recommended", I seem to be repeating myself here.
As far as accuracy of cut off is concerned, its all about testing components before using them.
One can wonder into the realm of "opinion" on this, with me the manufacturers data sheet is good enough.

I note the "no capacity between" commment above, I have graphs that I have prepared reflecting test results that indicate otherwise, but note my comment about slow death. Obviously a decreasing output will extend the burn time.
 

royfellows

Active member
and therein lies a tail as the water rat said to the , Oh never mind.


When I was young I had a Jag XK150 to which I fitted a new clutch. When I came to refill the gearbox I looked at the Jaguar manual and noted the recommended SAE 30 oil. I considered that this was a bit too thin and filled with SAE 90 gear oil.
The gearbox was noticeably quieter, I had got that bit right, but the overdrive didn't work. Mmm.
 

royfellows

Active member
Just a heads up that the project is back on the rails.
I have assembled some LED modules and just tried one with a redesigned controller. Basically, it works.
I do have more confidence in this one as I am using the driver IC that I originally wanted but stuck on back order until now. These are being used in the way they are intended whch I think gives one a head start.

I am now struggling with getting the values of shunt resistors working through Schottky diodes, not to mention that RSense value of the driver module affects the lower outputs as well. I am therfore reduced to the most basic form of exerimentation, that of "trial and error", plus the complex mental algorithm of guessometry.
 

royfellows

Active member
Some reasonably encouraging bench test results using the new driver chip. There are 4 brightness modes, this shows the lower two which are the most important. As commented before, the lower mode efficiency of most off the shelf buck drivers are poor.
 

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