Re: 1KV buck converter

On 25/05/2025 1:41 am, john larkin wrote:

On Sat, 24 May 2025 08:41:44 -0000 (UTC), piglet
<erichpwagner@hotmail.com> wrote:
 

Bill Sloman <bill.sloman@ieee.org> wrote:

On 24/05/2025 3:22 am, john larkin wrote:

On Sat, 24 May 2025 02:37:09 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
>

On 24/05/2025 1:05 am, john larkin wrote:

>
https://www.dropbox.com/scl/fi/f64mv46qk4g4nca00bgoe/1KV_Buck.jpg?rlkey=f0qnaliz7nyoowe6w4wx2gkua&raw=1

>
Anther one of John Larkin's pencil sketches - no resistances, no
inductances or capacitances and part numbers only for the transistors.

>
Uniball Vision ink pen, not pencil.
>

>
At least with an LTSpice .asc file you get that stuff automatically.
>
And you get some hint at the switching spikes, which can be nasty.

>
It's an idea. If you want a finished design, write me a purchase
order.

>
The guy who contacted me already had an idea the Baxandall inverter
would work. I'm still waiting for Infineon to come back to me with the
Spice model of their IMWH170R450M1 so that I can send him a simulation.
>
I won't charge him for it. If Infineon doesn't come through soon I'll
see if I can bodge an existing MOSFET model to match the SiC datasheet.
>
Whacky ideas including a Diac aren't going to open anybody sensible's
wallet. The kind of gullible sucker who would vote for Trump might go
for it.
>

>
Actually a Diac might make quite a good switch in an inverse Marx style
cascade voltage divider!

 Interesting. Gotta think about that one.
 Diacs are cool. I don't understand how they work. I've tried
simulating one with transistors but they don't unlatch. Must be some
silicon trick.
 I once needed to indicate the presense of high voltage without
dissipating a lot of power. An RC and a diac and an LED made a nice
bright 0.5 Hz flash with low average current.
 CCFL transformers usually have two windings with about a 100:1 ratio,
so it should be possible to make a sort of non-saturating blocking
oscillator, my buck topology but without the diac.  Maybe even rectify
a winding, a forward converter.
 Diacs come up to 380 volts and one amp, so one might use a diac as the
actual power switch in a buck or forward converter. Maybe even use two
in series.
 https://www.littelfuse.com/assetdocs/discrete-thyristors-kxxx0yh-series-datasheet?assetguid=89c51170-552a-4b3a-a3bd-287d64436e92
 You-know-who will hate the idea, as he instantly hates new ideas.

Diac and thyristors aren't new ideas. Diacs have been around since 1957, but nobody I've worked with has ever used them.
https://en.wikipedia.org/wiki/DIAC
points out that they are slow to turn on, and they turn off when the current through drops below the holding current.

Before there were IGBTs, there were megawatt power switchers,
converters and cycloconverters, that used enormous SCRs. That was
terrifying. At least diacs can turn themselves off.

They don't exactly turn themselves off - they just stop conducting when the current through them fall below the holding current - I could only find one data sheet that specified that and it gave a range from 10mA to 80mA. How long it took for them to turn off wasn't specified at all.
--
Bill Sloman, Sydney