Re: UCC33420 dc/dc converter eval

On 2025-04-10 13:56, john larkin wrote:

On Thu, 10 Apr 2025 12:36:34 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
 

On 2025-04-10 12:11, john larkin wrote:

On 10 Apr 2025 15:56:04 GMT, Uwe Bonnes
<bon@hertz.ikp.physik.tu-darmstadt.de> wrote:
>

john larkin <jl@glen--canyon.com> wrote:

On 10 Apr 2025 08:48:48 GMT, Uwe Bonnes
<bon@hertz.ikp.physik.tu-darmstadt.de> wrote:
...

I think this high frequency noise should be easy to filter by some CLC
Filter.

>
Not really. I need it to be close to the load, and that load is super
noise sensitive. I didn't check, but there is no doubt some
considerable and nasty emitted mag fields too.
>

>
Of course, the vincinity of any isolated DCDC is super noisy. If
nothing else helps, think about battery power.

>
I'm considering a bootstrap circuit to handle the switching power
assisted by a photovoltaic source for steady-state. I can bootstrap
off my own output pulse.
>

That sounds like fun--if you do that, please let us know how it works!

 The PVs are affordable and of course marvelously quiet, but they max
out typically below 100 uA. That gets tricky.
 I could consider a tiny supercap, assuming that my users won't try to
make weeks-long pulses.
 

>
>

>

>
In addition to all the high frequency crud, there's the basic burst
and its side effects in the hundreds of KHz range, would would take
giant parts to filter.

>
Look at LDOs with good PSRR at high frequency. From the datasheet, the
TPS7A20XX is still in the 40 db range at 1 MHZ. The LT1963 may be
better, but is much more expensive, the TPS7A20 is rather cheap and
available.
>

There are interesting parts around now that include their own power
isolation. Some are capacitive, not inductive, so may be better.
>

>
What part do you expect to have capacitive power transport? Capacitive
signaling is however common.
>
B.t.w, looking at a ISOW7841, I also see frequency in the 50 Mhz
range.

>
I suspect it uses similar power isolation as the UCCpart.
>

>
Wuerth WPME-CDIP Capacitive Digital Isolator Powered talks about 13 MHz

>
ADE9113 has power isolation too, and it also sounds magnetic. I
thought I saw a capacitive power isolator somewhere.
>

>
Jim Williams used to write about piezoelectric transformers, back in his
CC-fluorescent backlight days.  (May they never return--fluorescent
lights suck eggs.)

 I always thought the piezo transformer was cute. The real HV isolator
is a motor and a generator and a fiberglass shaft, all surface-mount
of course.
 I  threw out a bunch of incandescent bulbs and wish I'd kept a few. I
don't miss CFs at all.
 

I have a couple of old Luxo adjustable desk lamps that I love--one at my drafting table and one at my workbench.  They have a medium-base light socket surrounded by a 22-W circline fluorescent tube.  I mostly use LED bulbs, but for testing things like photoreceivers, where the 40-kHz flicker is obnoxious, I have a medium-sized stock of 100-W, 1690-lumen tungsten bulbs that I collected back in 2012.
I'll happily send you a couple of packages if that would be useful.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510
http://electrooptical.net
http://hobbs-eo.com