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Question for driving gate on mosfets

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filippos_ineglis

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schem.jpgN-mos.jpgDC_sweep.jpgHello,
I'm trying to drive the gates of two N-mosfet for a class D amp(2N6661). I have Vrail(+)=70V connected to the drain of the high mosfet and Vrail(-)=-70V connected to the source of the low side mosfet(snapshot 1). To drive them fully on I have to apply +-90V to both gates. Is this normal? Is there any IC that does this thing?
There is also a simpler circuit of this mosfet(snapshot 2) and its DC Sweep simulation(snapshot 3).
There migth be some serious mistakes, they are my first tries.
 

Each of the NMOSFETs wants to be driven, relative to
its source terminal, by about 10V (unless these are some
"logic level" FETs).

The low side FET wants -70 (off) and -60 (on). Its source
is pinned to the -70V rail.

The high side FET wants -70 (off) and +80 (on) because
the source is flying and the drain is pinned.

Driving it +/- 90V will work in simulation, but fry you up
a whole pan of crispy gate oxide in real life.

Now why you'd go and put 50 ohm series resistors and
use such a high supply, when you could get about the
same effective drive to the load using no 50 ohm
resistors and +/-12V or so, eludes me. Other than
maybe limiting the shoot-through current, which you
should do on the control (gate drive) end instead if
you wanted efficiency better than 20%.
 
Hello,
thank you for your fast responce. I put the 50 ohm resistors to increase the damping factor, without taking into consideration the efficiency because I forgot it. I put a snapshot of a simpler circuit and a second snapshot of the output. It seems to work fine. The problem now is how to produce these voltages for gates. I will use an IC or BJT?
schem.jpgoutput.jpg
 

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