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Subject: Re: [geda-user] (Off-topic) Question wrt driving HV piezo transducer
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From: "Richard Rasker (rasker AT linetec DOT nl) [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com>
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Date: Sat, 17 Feb 2018 21:40:17 +0100
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Hello John,

Op 17-02-18 om 18:29 schreef John Griessen (john AT ecosensory DOT com) [via 
geda-user AT delorie DOT com]:
> On 02/17/2018 05:28 AM, Richard Rasker (rasker AT linetec DOT nl) [via 
> geda-user AT delorie DOT com] wrote:
>>
>> Ah, I understand now. As mentioned, I only need 41 kHz, as that is 
>> the f0 of the transducer.
>
> You may not be able to drive all that power at 2500V, certainly not 
> easy with a doubler sagging down,
> Do you really need to measure that fast?  If not, then the switching 
> speed can be 80 or 60 or 50 kHz, and
> maybe 6 of those needed to ramp up to near 2500V then settle 
> accurately on a valued for measuring position
> such as 2330V.  So overall response time would be about:  72 
> microseconds.  (13.8kHz rep rate.)

Hm, I'm not sure if we still have a serious misunderstanding here... 
Here's the complete specification:

Transducer:
f0: 41 kHz
C0: 5nF +/-20%
Vpp-max: 1800V

Intended drive signal: 1 - 1.5 ms bursts (so 40-60 periods) @ 1500Vpp, 5 
Hz repetition rate.

> I also found this calculator: 
> http://www.dicks-website.eu/coilcalculator/index.html
>
> Yep, that's what I used.

I selected a 3C90 Ferroxcube core (the ETD29/16/10-3C90) and filled in 
the following values:
Bmax = 0.2T (rather lower than the specified 330mT max, to be on the 
safe side)
Cross-section = 76 mm²
mu-e = 1770
Al = 2350 nH/n²
=======
12V RMS in
600V RMS out (=~ 1700Vpp)
f = 41000 Hz
-> 5 turns primary, 250 turns secondary
=======
Primary wire diameter: 0.5 mm
Secondary wire diameter: 0.05 mm
Length per turn primary: 35 mm
Length per turn secondary: 35 mm
Load resistor: 2K

This produces still workable values for primary input current (~14A) and 
losses at a decent output voltage.

[offer for sending me some rejects]
Well, thank you, that is very kind! But I think I'll go with the 
selected 3C90 core set and try to build my own transformer.
Not only will it no doubt be a valuable experience, I can tune it to the 
exact desired specifications, whereas your devices probably have a too 
high output voltage, and I doubt if I can disassemble them to take off 
some of the secondary.

I will need to be careful about secondary insulation of course, but from 
what I see, the bobbin offers room for a few (improvised) chambers.

One thing is certain: HV transformers are almost an art and a science in 
and of themselves...

But thanks again,

Best regards,

Richard