Re: UCC33420 dc/dc converter eval

On 15/04/2025 13:47, Chris Jones wrote:

On 14/04/2025 3:40 am, Carl Ijames wrote:

On Sun Apr 13 23:06:25 2025 Chris Jones  wrote:

On 12/04/2025 1:12 am, john larkin wrote:

On Fri, 11 Apr 2025 23:31:24 +1000, Chris Jones
<lugnut808@spam.yahoo.com> wrote:
>

On 11/04/2025 3:56 am, john larkin wrote:

The PVs are affordable and of course marvelously quiet, but they max
out typically below 100 uA. That gets tricky.

>
You can get more powerful ones for "power over fibre" with a laser at
the other end. I vaguely remember there being an example in AOE3.

>
I would love such a power optocoupler, if it were a reasonable size
and price.
>
There must be a market for a really quiet isolated dc/dc converter.
Maybe a sine wave thing.
>

[snip]
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Yes I have been thinking about that, a really quiet DC-DC, e.g. with a
magnetically-shielded transformer having both windings thoroughly
electrostatically screened, or an optical isolator (but there is a worse
limit to the efficiency for optical). The DC-DC inside Keithley
Sourcemeters is interesting in its construction though I have no idea
how well it performs.
>
Solar cells are cheap, and high-power IR LEDs are fairly cheap too, but
the combination won't be super-efficient nor small. If you want to avoid
putting multiple solar cells in series, you could connect one solar cell
to a step-up transformer, and modulate the LED current so that there is
some AC for the transformer to step-up. To avoid DC in the windings you
could even put two solar cells in anti-parallel across the low voltage
winding of the transformer, and illuminate the pair of solar cells
separately with two IR LEDs driven with opposite phase AC. Big solar
cells have a lot of capacitance though, so the frequency would have to
be lowish. If you want more isolation voltage, the light could be guided
through a acrylic rods like a fat optical fibres. It'd be large, and not
as efficient as a transformer.

>
If you hermetically seal the entire assembly in a metal box with feedthroughs, you could use perovskite solar cells for a nice bump in efficiency to lower the total area of cells you would need, and have great EMI shielding.  Just include a little pkg of silica gel in the box to soak up moisture and the perovskites should last longer than you need them to.

 If you can choose the wavelength of illumination, there is no need to use perovskites, as their ability to be tuned to match the spectrum of sunlight has little benefit. I work with perovskite cells that stay in a glove box full of very pure nitrogen (not me, I stay outside in the air). Lots of things damage them, though they are getting better.
 Interestingly, white LEDs don't like being inside the glove box in pure nitrogen. They rapidly lose efficiency if they are operated in there, but they recover if a little bit of oxygen is added (which we can't do, because it harms the perovskites). So the LED solar simulator has to stay outside. It has dozens of different LED wavelengths, some of them are not bothered by being in nitrogen.
 With an optical power isolator, the area of solar cells can be kept small if the illumination can be prevented from spreading out much. So, if a laser diode puts a few watts down a fibre, the receiving cell could be tiny, perhaps only limited by not wanting it to melt.
 

It would be possible to couple a single high-powered fibre laser
to several photodiodes - perhaps connected in series to get a
more useful voltage - using a fibre beam splitter.  Such
splitters are very cheap if you choose an infra-red wavelength
compatible with passive optical networking (GPON or XGPON) .
John