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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
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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