On a sunny day (Fri, 16 Feb 2024 17:04:17 -0000 (UTC)) it happened "Don"
<
g...@crcomp.net> wrote in <
2024...@crcomp.net>:
>Jan Panteltje wrote:
>> Don wrote:
>
><snip>
>
>>>The TL431 needs to be repurposed into a power supply before my crystal
>>>set can accommodate another adornment: an audio amp in the form of a
>>>LM386. It turns out the power supply in my "bone yard" chassis supplies
>>>only 5 VDC.
>>>
>>>So a simple SMPS, similar to the flyback converter Win Hill reversed
>>>engineered for Figure 9.74 in _Art of the Electronics_, needs to be
>>>prototyped:
>>>
>>><
https://archive.org/details/the-art-of-electronics-3rd-ed-2015_202008/page/657/mode/2up>
>>>
>>>Applications found in both the CSC72XX and UC3843 datasheets also fit the
>>>bill.
>>
>> I am wondering, would not a non-switching converter (mains transformer +
>> rectifier followed by maybe a LM317) give less RFI?
>
>Your assessment's absolutely accurate (according to my gut). Regardless,
>my tinkering involves more than one goal, and fiddling with SMPS along
>the way is acceptable.
>
>And any advice about DIY SMPS transformers from readers is appreciated in
>advance.
It is hard to do better than the small wall-warts that you can buy for just a few dollars.
Those use advanced chips with all sorts of protections, are often CE certified
saving you a lot of work, safer too:
https://www.panteltje.nl/pub/floor_warts_IXIMG_0790.JPG
For the switchers I designed I usually use a Microchip PIC as driver chip,
it has 2 build in hardware comparators that you can use for cycle by cycle current limiting
and it has several ADC channels, needs programming though.
As a rule of thumb for transformers: 1V per turn for 15 kHz switching frequency
for small transformers like this one:
https://panteltje.nl/pub/new_transformer_test_setup_img_3153.jpg
But look for inductance, core material, possible air-gap, current, DC bias, frequency, etc etc.
Or grab one from an old defective wall-wart?
Switchers have a lot of negatives, yesterday I repaired a satellite receiver box that had, among several other
regulators, a 5V switcher for the memory and CPU chips and USB memory stick.
it would abort recording on random occasons.
Super small box, the one on the right, rather new:
https://panteltje.nl/pub/sat_box_sizes_IXIMG_0907.JPG
was thinking as it got worse over time, could be a filter cap in one of the switchers.
Opened it and scoped the ripple on the filter caps:
about 1.5V RF spikes on the 5V output cap.
Replaced cap, with one from the junk box, recording works again....
Need to get some low ESR caps, and maybe bias it with a better smaller capacitor.
But even then the thing runs of a 12 V wall-wart... with overload protection.
If you want to get a bit bigger, then get an old PC power supply [transformer],...
Plenty of circuits for that online too.
I often use what I find laying about in the junk box...