Re: An extremely good MOSFET driver

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

Original poster: "K. C. Herrick by way of Terry Fritz <twftesla-at-qwest-dot-net>" <kchdlh-at-juno-dot-com>

Daniel, Dave Sharpe, Malcolm Watts (& all)-

Comments interspersed...

On Tue, 06 Aug 2002 22:03:43 -0600 "Tesla list" <tesla-at-pupman-dot-com>
writes:
> Original poster: "Daniel McCauley by way of Terry Fritz 
> <twftesla-at-qwest-dot-net>" <dhmccauley-at-spacecatlighting-dot-com>
> 
> 
> This circuit shown below:
> 
> http://www.spacecatlighting-dot-com/datasheets/mosfetdriver.pdf
> 
> is an extremely fast mosfet driver circuit ...

[snipped]
> 
> BTW, why would you want to turn on your MOSFET slowly???  Doing this 
> will
> most likely put the FET in its linear operating range and start 
> really
> heating it up.  You want something really fast.
> 
> Dan

[snipped]

I'd love to turn them both off & on blazingly fast...except that if I do
that with any given pair of them, then both transistors of the pair find
themselves on at the same time while one is turning off & the other, on. 
That shorts out the power supply during that instant of time.  I notice,
in your circuit, the other secondary winding, and suppose that it drives
an identical MOSFET circuit, which perhaps is in a 1/2-H configuration
with Q1.  Do you not have that problem?

Other than that, the scheme is surely OK.  Have you considered using a
paralleled-gate CMOS logic IC in place of the two bipolars?  Or are the
older 15V-rated ICs becoming obsolete, nowadays?

Re David's comment:

"I've always been told to NEVER forward bias a zener diode,
you will hose its knee characteristics.  Comments from the
list???
 
Regards
Dave Sharpe",

I've never heard that although I have heard it about bipolar base:emitter
junctions, as to degrading the transistor's gain--but I don't know if I
believe it.  I have an old Motorola Zener Diode Handbook that goes into a
lot of detail and there's no mention in it of that kind of problem. 
Anyone else have info?

As to Malcolm's comment re gate resistors--yes, I'd want 10 ohms or so in
series with the gate(s) for parasitic suppression, and also a pull-down
resistor, gate:source, for Q2.  Also, the transformer might need a load
resistor.

Ken Herrick