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Path: news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail From: John R Walliker <jrwalliker@gmail.com> Newsgroups: sci.electronics.design Subject: Re: UCC33420 dc/dc converter eval Date: Tue, 15 Apr 2025 15:17:58 +0100 Organization: A noiseless patient Spider Lines: 75 Message-ID: <vtlpqm$37401$1@dont-email.me> References: <qerdvjtlphmh0hfkec83dqsh9h88vlgp29@4ax.com> <m5pevgF8ic0U1@mid.individual.net> <fiofvjt8a5kvjtfomf7dro81hh9tkpocjd@4ax.com> <m5q80kFcad2U1@mid.individual.net> <dqqfvj519hornismnvc3s8kstv1a49bs5g@4ax.com> <ffda6ad6-a2ba-a540-7e0b-abdfbb50dbdf@electrooptical.net> <orufvj9soq65j1c4rqmcl1ik84llk02k8u@4ax.com> <OQ8KP.1226743$cgs7.566726@fx14.ams4> <robivjlb5pfnffq8n0h7n6ul0ihumc1k37@4ax.com> <oFOKP.468698$X61.184749@fx07.ams4> <dGSKP.1830293$OrR5.1452967@fx18.iad> <KzsLP.2443928$nb1.2404703@fx01.ams4> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Injection-Date: Tue, 15 Apr 2025 16:17:59 +0200 (CEST) Injection-Info: dont-email.me; posting-host="871bf3eb598c8013c8c366997c81416c"; logging-data="3379201"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX19aWhkeOU64uvpCohUhWH0764ueKzpr4iw=" User-Agent: Mozilla Thunderbird Cancel-Lock: sha1:QcuGhxtMplJ4XAUsK6P1Wi1UfHk= Content-Language: en-US In-Reply-To: <KzsLP.2443928$nb1.2404703@fx01.ams4> 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] >>> >>> 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