Re: SSTC, xfmr gate drive oddity

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

Original poster: "John Tomacic by way of Terry Fritz <twftesla-at-qwest-dot-net>" <tesla_ownz_u-at-hotmail-dot-com>


Hi,
I believe you only need z1 and z4. z2 and z3 are shorted out as drawn in 
your diagram.

Regards,
John


>From: "Tesla list" <tesla-at-pupman-dot-com>
>To: tesla-at-pupman-dot-com
>Subject: Re: SSTC, xfmr gate drive oddity
>Date: Thu, 06 Jun 2002 07:09:35 -0600
>
>Original poster: "Jan Wagner by way of Terry Fritz <twftesla-at-qwest-dot-net>" 
><jwagner-at-cc.hut.fi>
>
>
> > Original poster: "Malcolm Watts by way of Terry Fritz
><twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>
> > If you are really set on doing this with FETs, you will need to
> > ensure that they cannot turn on together. You can approach this by
> > using a 2-zener series string between the gates and driving the
> > zeners at their junction.
>
>Like this?
>                    Vdd
>                     |
>                 ||--+ source
>     +--+--|>|---||     p-channel
>     |  |   Z1   ||--+ drain
>     |  ^            |
>     |  - Z2         |
>     |  |            |
>----+  |            |
>     |  |            |
>     |  - Z3         |
>     |  V            |
>     |  |   Z4   ||--+ drain
>     +--+--|>|---||     n channel
>                 ||--+ source
>                     |
>                    GND
>
>(hope it doesn't get garbled up... use a fixed font to view!)
>
>Hmm the zeners there are probably all the wrong way round...? Or are they?
>Also, what v_br voltage should the zeners have? around 5V?
>
> > Bipolars will not exhibit this problem in
> > the original arrangement with their bases tied together.
>
>I tried looking for fast, high current, low voltage, low V_ce_sat & low
>V_be bipolars.
>
>There are many "selection guide" lists around, but all the more commonly
>available bipolar transistors for this task seem to have microsecond range
>rise&fall times, i.e. much too slow to drive fets? Also, horrible V_ce_sat
>voltages...
>T.ex. the NPN BD909 seems otherwise nice and common but V_ce_sat~=3V and
>for BD910 (NPN) V_ce_sat~=6V.
>
>Maybe someone who has already built a high peak current gate drive
>with bipolars could help me out and suggest some non-exotic
>bipolars that would be suitable?
>
>I.e. ~24A peak >40V NPN+PNP transistors that could switch at <=300kHz
>"cleanly" with <100ns rise and fall times?
>
>Though I'm starting to doubt this is possible at all... ?
>
>
>many thanks,
>
>  - Jan
>
>--
>*************************************************
>  high voltage at http://www.hut.fi/~jwagner/tesla
>
>
>