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From: Bill Sloman <bill.sloman@ieee.org>
Newsgroups: sci.electronics.design
Subject: Re: 1KV buck converter
Date: Sun, 25 May 2025 04:08:28 +1000
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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