Post by Jan PanteltjePost by Don<snip>
Post by Jan PanteltjePost by DonThe 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
<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
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
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.
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.
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...
My mindset mostly mirrors yours. Here's the story so far:
The chassis came from my bone pile. Its NEMA grounded bulkhead
connector enables an easy connection from a proto-board to ground.
Adding an audio amp along the lines of a LM386 seemed a fitting way
to wrap up the AM receiver before moving on to FM. Unfortunately the
chassis' built-in SMPS only outputs a meager 5 VDC instead of the 12
VDC or, better yet, 24 VDC sought by me.
A quick rummage through my surplus wall warts (over a hundred in
all) unearthed a 12 VDC jewel. The plan was to liberate its board from
its plastic enclosure then swap it into the chassis in place of the
built-in. But the jewel's board didn't cooperate - its footprint was
too small to accomodate the chassis' SMPS mounts.
The jewel seems like simplicity itself. It's scarcely more
complicated than the typical 555 circuit:
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Why not assemble a similar circuit from spares on a larger universal board
and also mod it to output 24 VDC?
# # #
Alternatively, all analysis and reverse engineering can be avoided by
using AI to design it:
PI Expert is an automated, graphical user interface (GUI)
driven program that takes power supply specifications and
automatically generates a power conversion solution designed
around the most appropriate Power Integrations’ IC family.
PI Expert provides all necessary information to build and
test a working prototype, including the full schematic and
BOM. PI Expert also provides a complete transformer design
that includes core size, number of turns, appropriate wire
selection and winding construction. Detailed winding
instructions for mechanical assembly are also generated.
<https://pi-expert-suite.software.informer.com/download/#downloading>
Danke,
--
Don, KB7RPU, https://www.qsl.net/kb7rpu
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.
