Re: S.s. MOSFET-driving

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Kchdlh-at-aol-dot-com>

In a message dated 12/30/2001 2:22:05 PM Pacific Standard Time,
tesla-at-pupman-dot-com writes:


>
> Subj:Re: S.s. MOSFET-driving 
> Date:12/30/2001 2:22:05 PM Pacific Standard Time
> From:<mailto:tesla-at-pupman-dot-com>tesla-at-pupman-dot-com
> To:<mailto:tesla-at-pupman-dot-com>tesla-at-pupman-dot-com
> Sent from the Internet 
>
>
>
> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
>
> Hi Ken,
>
> You may want to see Marco's discussion of IGBT drive problems and fixes at:
>
> http://personal.inet.fi/atk/dncmrc/
>
> I found that I needed series resistance (100 ohms) to slow down the IC's
> switching speed or they would blow the IGBTs.  The IC designers wanted to
> force
> the gate capacitance to the voltage they want instantly and they did a bit
> "too" good of a job ;-))  That is the only trouble I ran into but I don't
> have
> transformers and such (fiber optic).
>
> Cheers,
>
>         Terry
>
>
> At 01:31 PM 12/30/2001 -0500, you wrote: 
> >
> > There's been mention made recently of the IR2110-series ICs for driving
> > Tesla-coil MOSFETs.  A long while back I had intractable trouble using
> those
> > ICs, seemingly because the very high-impedance voltage-translating
> circuitry
> > within the IC was being affected by the coil's electric field.  I had to
> get
> > rid of the IC-drive scheme and go to discrete-component drivers + isolating
> > transformers.  For the latter, I just use readily-available common-mode
> > chokes (2 windings on a toroid) connected as 1:1 transformers.
> >
> > And as to the transformer-drive...I additionally found a problem in that,
> > every time drive was cut off at the termination of a spark-event, the
> > transformer's flux would have to reset to 0 and that would cause the
> MOSFETs
> > to turn on spuriously.  I had to add additional circuitry to eliminate that
> > turn-on.
> >
> > Ken Herrick
>
>
>



Terry-

Thanks for the tip; I'll check it out.  It's likely that the 100 ohm resistor
damps out destructive oscillation, which will occur when the low-Z and very
fast drive signal meets up with the MOSFET's gate capacitance.

Ken