Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail From: John R Walliker Newsgroups: sci.electronics.design Subject: Re: UCC33420 dc/dc converter eval Date: Wed, 16 Apr 2025 15:24:52 +0100 Organization: A noiseless patient Spider Lines: 92 Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Injection-Date: Wed, 16 Apr 2025 16:24:52 +0200 (CEST) Injection-Info: dont-email.me; posting-host="4d477a42059a30c11df944b45656ff58"; logging-data="1778012"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX18jo20jlyZi5fcELK794dAARpS/lNy3Sys=" User-Agent: Mozilla Thunderbird Cancel-Lock: sha1:tfb0Z159YjVkgelCOfhPZ6Jp7zw= In-Reply-To: Content-Language: en-US Bytes: 6181 On 15/04/2025 19:40, Joe Gwinn wrote: > On Tue, 15 Apr 2025 15:17:58 +0100, John R Walliker > wrote: > >> 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 >>>>>> 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 > > Solar cells are silicon, which don't work at all with wavelengths > exceeding 900 nanometers, or shorter than about 500 nm. > > Joe Yes, but there are fibre-coupled detectors that work at longer wavelengths. The only reason for using long wavelengths is that there are lots of low-cost parts around (including fibre splitters) that are used in GPON networks. The voltage per diode will of course be lower with long wavelength devices. John #