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From: john larkin <jl@glen--canyon.com>
Newsgroups: sci.electronics.design
Subject: Re: LTSpice model for a SiC MOSFET
Date: Tue, 27 May 2025 07:47:39 -0700
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On Wed, 28 May 2025 00:28:12 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:

>On 27/05/2025 11:46 pm, john larkin wrote:
>> On Tue, 27 May 2025 14:16:11 +0100, liz@poppyrecords.invalid.invalid
>> (Liz Tuddenham) wrote:
>> 
>>> Bill Sloman <bill.sloman@ieee.org> wrote:
>>>
>>>> On 27/05/2025 9:09 am, john larkin wrote:
>>>
>>> [...]
>>>>> The specs, as far as I can tell, suggest 1KV at 1 ma in and 3.3v at 3
>>>>> ma out. The required efficiency is then 1%.
>>>>
>>>> Actually 1kV at 10uA in.
>>>
>>> Good grief!   A 10-megohm quarter watt resistor with a zener diode is
>>> the obvious answer.
>> 
>> A 3.3v real zener will probably leak more than 10uA. Low voltage
>> zeners are awful.
>> 
>> And he wants 3 mA out... I think.
>
>The guy I was talking to had 10uA at 1kV, and wanted a 3.3V output. 1mW 
>at 3.3V is 3mA. The 3ma is the upper limit the circuit could supply.

Geez, check your work before you post it. 3.3v * 3 mA is 10 mW.

I have a few kids that I'm teaching to design electronics. They
already have EE degrees.

One of the fundamental concepts: check your work.

>>>
>>> [...]
>>>> Misunderstanding the constraints can lead people to propose
>>>> inappropriate solutions.
>>>
>>> How can anyone misunderstand something they have never been told?
>
>You managed it.
>
>> Bill was the confused person.
>
>John Larkin does like to think that.
>
>> The problem gets much more interesting with 10 uA in and 99%
>> efficiency requirement.
>
>There never was an efficiency requirement. 50% would have been nice.
>
>> A Baxandall isn't going pull microamps at 1 KV.
>
>Keeping a resonant tank resonating at a couple of kV is going to use up 
>power in the winding resistance. I think I can get 245H out of RM14 
>core. If we can keep the parallel capacitance down to 25pF that would 
>resonate at 2kHz and the reactive impedance would be 3 Mohm, giving a 
>peak current 0f 1mA. The resistance of the winding is going to be about 
>480R, so I^2.R is 500uW, or 0.5uA at 1kV.
>
>A properly designed Baxandall might well pull less than 1uA if lightly 
>loaded.

Build it.