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: Wed, 16 Apr 2025 15:14:33 +0100
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On 15/04/2025 19:40, Joe Gwinn wrote:
> On Tue, 15 Apr 2025 15:17:58 +0100, John R Walliker
> <jrwalliker@gmail.com> 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
>>>>>> <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
> 
> Solar cells are silicon, which don't work at all with wavelengths
> exceeding 900 nanometers, or shorter than about 500 nm.
> 
> Joe

The camera in my phone just about responds to 850nm.
However, there are plenty of 1310 and 1550nm fibre-coupled
photodiodes around.
Whether they would survive more than a few tens of mW is another matter.
John