I am designing a high side driver to go with a low side driver to form  
1/2 of an H-bridge.
I am using 1500V MOSFETs ( STW4N150 )
http://www.st.com/stonline/products/literature/ds/11262/stp4n150.htm
The spec says the turn on and turn off time for this MOSFET is about  
50 nsecs.

I have considered using an opto-isolator part.  Are there any that  
have a speed around 50 nsec ?
Or are there any other isolation techniques that would work ?


I have included two schematics that show an approach I am considering.
http://oh-god.com:5080/dir/1500V-driver/

the first schematic shows a totem pole consisting of two MOSFETS with  
drivers.
HSD ==> High Side Driver
LSD ==>  hallucinations , I mean Low Side Driver


The second diagram is a High Side Driver.  Isolated 12V is supplied to  
drive the MOSFET.  R1 is 50K.
Reflected through Q1 ( 2N3906 PNP )  ( I forgot the arrow on the R1  
side of Q1 )  , the base of Q1 will see
5M ohm.  R2 is 5M ohm.   The Q2 MOSFET is a 1500V device.  D2 would be  
a 1N4148 and D1 is a 15V zener.
D1 is there to guarantee that none of the parts sees more than 15V.  
( Other than Q2 or R1 and R2 )
Power dissipation through R1 and R2 should be less than .25 watt.

Turning on Q2 should turn Q1 off.

A 2N3906 is rated at 100 MHz.   A 1N4148 is much faster than a zener  
diode ( I think ).

Will this circuit blow up and put out my eye ?

images are hand-drawn schematics captured by PhotoBooth running on a  
MacBook.

Gus


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