> On 7/28/2011 12:09 AM, RussellMc wrote:
>> First suggestion is a speedup capacitor across RB.
>> Comment on that and we can go from there.
> Played with different values and basically increased the value until
> there was no appreciable difference in turnoff speed. =A0Basically right
> now I have a 0.022 =A0or thereabouts across the 1K base resistor. =A0 And=
 no
> gate resistor on the big P channel mosfet (to eliminate that variable).


Djula' driver deals with switching time of Q1 but you still have R2
passively pulling the driver bases high.

With the addition one or possibly two transistors (which cost almost
nothing) you can get active positive going (=3D turnoff) drive to the
driver pair which should help immensely. Gate resistor is then usually
the speed setter.

Once you have active  turnoff drive you can find two points "which go
the same way at the same time" and add some positive feedback between
them.

> It's late so I'm going to ask the potentially stupid question my mind
> isn't processing right now very well.. since this produces a negative
> gate pulse as the 3.3V input goes to zero... is there a 'too big' of
> value for this that will cause damage to the level shifting transistor?

I'd not expect any value of capacitor you were liable to want to use
would cause any damage.  You can check the power levels but they
should be minimal.
 (1/2 x C x V^2 x f).


    Russell

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