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HV design problem

P

Peter Andersen

Jan 1, 1970
0
Hi



I have done some experimenting with a HV power supply design. I have posted
my regulation design here: www.mespilus.dk/HV.pdf



The problem is this when I reach about 270V output it starts to oscillate
and I have some very nice sinus curves at the output. Under and over 270
there is no problem.



I tried to follow the example in AoE page 372 and placed some caps (100nF)
on the divider resistors but that blew the first to of my fets.



Any help?



Peter
 
J

Jim Thompson

Jan 1, 1970
0
Hi



I have done some experimenting with a HV power supply design. I have posted
my regulation design here: www.mespilus.dk/HV.pdf



The problem is this when I reach about 270V output it starts to oscillate
and I have some very nice sinus curves at the output. Under and over 270
there is no problem.



I tried to follow the example in AoE page 372 and placed some caps (100nF)
on the divider resistors but that blew the first to of my fets.



Any help?



Peter

As a start... what limits G-S voltage?

...Jim Thompson
 
P

Peter Andersen

Jan 1, 1970
0
Jim said:
As a start... what limits G-S voltage?

I know the right way to do it is with zeners. In this one I just use
1N4148 - but surely that couldn't have anything to do with this problem? in
the final design I will off cause have some zeners!



Peter
 
J

Jim Thompson

Jan 1, 1970
0
I know the right way to do it is with zeners. In this one I just use
1N4148 - but surely that couldn't have anything to do with this problem? in
the final design I will off cause have some zeners!



Peter

All the 1N4148's are doing is limiting reverse G-S voltage, NOT
forward.

If you are exceeding 20V G-S who knows what may be happening.

Put zeners in there NOW!

...Jim Thompson
 
R

Robert Baer

Jan 1, 1970
0
Peter said:
Hi



I have done some experimenting with a HV power supply design. I have posted
my regulation design here: www.mespilus.dk/HV.pdf



The problem is this when I reach about 270V output it starts to oscillate
and I have some very nice sinus curves at the output. Under and over 270
there is no problem.



I tried to follow the example in AoE page 372 and placed some caps (100nF)
on the divider resistors but that blew the first to of my fets.



Any help?



Peter
1) Why don't you drive the 100K divider and first FET gate from the
"pulldown", dispensing the 470K chain?
2) Why don't you use one FET?
 
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