Re: An extremely good MOSFET driver

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

Original poster: "Daniel McCauley by way of Terry Fritz <twftesla-at-qwest-dot-net>" <dhmccauley-at-spacecatlighting-dot-com>




Disagree you must I guess.  However, this MOSFET drive circuit is the
backbone gate driver in a high powered DC-DC converter used to power antenna
line arrays in the Aegis Radar system found on US Naval Destroyers.  Been in
service for many years now and never any problems.

Dan

Actually, you probably are correct in that there is always the forward
voltage drop of the junction present each cycle, however
with the FETs we used, this is not a problem and is just a very small
trade-off for a very fast gate driver.



> Dan (& all)-
>
> I'm afraid I still have to disagree:  If Q6 is an ordinary PNP biploar,
> it has a diode junction between base and collector that will conduct in
> its forward direction when the base is negative with respect to the
> collector.  That condition is surely going to happen every 1/2 cycle.  I
> believe Q6 needs a base resistor.  Once you were to provide that, you'd
> need a diode across Q5's b:e junction to keep that from zenering.  Or,
> just put the resistor in series with the lead from the transformer and
> keep the bases tied together.
>
> KCH
>
> On Fri, 09 Aug 2002 11:53:05 -0600 "Tesla list" <tesla-at-pupman-dot-com>
> writes:
> > Original poster: "Mccauley, Daniel H by way of Terry Fritz
> > <twftesla-at-qwest-dot-net>" <daniel.h.mccauley-at-lmco-dot-com>
> >
> > > This circuit shown below:
> > >
> > > http://www.spacecatlighting-dot-com/datasheets/mosfetdriver.pdf
> > >
> > > is an extremely fast mosfet driver circuit...
> >
> > [snipped]
> >
> > Whoa!...I took a closer look:  Dan, am I missing something or do I
> > see a
> > problem with Q6?  Each time the transformer-secondary voltage
> > becomes -
> > on top & + on the bottom, does not Q6's base:collector junction
> > become
> > forward biased?  That's going to ruin the other secondary's output,
> > when
> > it's (presumably) trying to turn on its MOSFET.
> >
> > Hmmm...
> >
> > No.  When the gate transformer is "positive", Q5 turns on and Q1
> > get
> > "slammed" on.  At this time, C28 also
> > charges up.  When the gate transformer goes "negative", Q5 turns
> > off, Q6
> > turns on and with the help of C28, allows
> > the gate capacitance of Q1 to discharge very fast and thereby
> > turning off Q1
> > very fast.
> >
> > Dan
> >
> > When working on a prototype version of my SSTC#1, I used this
> > circuit in a
> > half-bridge and got almost perfectly square (rise / fall times <
> > 100nS) gate
> > drive waveforms up to about 450kHz. However, this circuit does
> > dissipate a
> > bit of heat - thats for sure.
> >
> > Dan
> >
> >
> >
> >
> >
> >
>
>
>
>
>