Mail Archives: geda-user/2018/02/16/09:33:50
On Friday 16 February 2018 06:38:48 Richard Rasker (rasker AT linetec DOT nl)
[via geda-user AT delorie DOT com] wrote:
> Hello Marcel,
>
> Op 16-02-18 om 06:32 schreef mhx AT iae DOT nl:
> > On 2018-02-15 23:02, Richard Rasker (rasker AT linetec DOT nl) [via
> > geda-user AT delorie DOT com] wrote:
> > [..]
> >
> >> However, this afternoon, the product dealer was kind enough to send
> >> me the schematic of a 500 Vpp development driver kit, featuring a
> >> center-tapped symmetrical push-pull transformer(*) circuit with two
> >> FDD16AN08 MOSFETs, each with a 1 uF capacitor across drain-source.
> >> These big DS-caps seem rather weird already.
> >
> > [..]
> >
> > This could be a push-pull parallel-resonant parallel-load type
> > configuration.
> > It should be tuned to exactly the resonance of the effective L+C and
> > will have
> > a Vds of about 3.14159 times the supply voltage. The transistors
> > turn on when
> > their Vds tries to go negative (automatically). The 1uF across drain
> > source does
> > not sound familiar but is equivalent to a single cap between the two
> > sources,
> > i.e. in parallel to the transformed transducer (as it should be).
> > Theoretically, this is the dual circuit to the HB series resonance
> > series load
> > one.
>
> Thanks for the explanation, although I don't quite grasp the
> theoretical basis -- I'm not very experienced with transformer
> circuits, and this one in particular still raises some questions. Can
> you point to some other examples where this principle is used? Most
> CFL drivers I find employ some sort of series resonance solution,
> AFAICT, without any DS caps.
>
> For all clarity, I attached the schematic, also because there's
> something else I don't understand: the top MOSFET (Q1) doesn't get the
> burst frequency at all, just the 1.5 ms LF pulses. The bottom one (Q2)
> is supplied with the burst signal as expected.
>
> I carefully checked this against the schematic I was given, and I'm
> positive that I didn't make a mistake here. Could this be a mistake on
> behalf of the original designer? I contacted the supplier, but they
> couldn't tell me anything. Or perhaps Q1 is 'automatically' syncing to
> Q2 via changing voltage levels on the drain? I can't really see this
> happening in any reliable way...
>
> BTW, the circuit isn't really designed for resonance, as the 41 kHz
> given is in reality a selectable frequency between 3 kHz and 300 kHz,
> with 41 kHz being just one of the settings.
>
41 kilohertz is the frequency used by older burglar alarms.
But they ran a continuous tone, and detected the change in the rooms
standing waves that a body moving around caused. I have Carhart notches
120+ db deep in both ears, but those things give me a tight feeling in
both ears, annoying enough that I've been known to vacate the area w/o
making a purchase. So I wouldn't be surprised to see a similar piezo
device used here. The are also lots of ultrasonic parts cleaners that
run at that frequency, altho I faintly recall one that claimed 90
kilohertz I saw recently, a 1/2 gallon model IIRC.
Since a custom unit would cost more, 41 kilohertz is probably the sweet
spot priced unit.
> Anyway, thanks for all your help so far (from the others too), I'm
> learning a lot!
> (And I think I'd better start calculating, building and measuring
> things now.)
>
> Best regards,
>
> Richard
--
Cheers, Gene Heskett
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>
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