low voltage controlled high voltage

[sdouble]

hi guys,
I have a question for you.
Here is my trouble.
I have a charge integrator with a FET input.
I have a AC coupling to the sensor since I bias it to about 500 V.
In the current design, if an idiot (could be me) turn on the high voltage without low viltage to bias the FET... boom.
The FET dies.
Therefore, I would like to condition the HV to the presence of the Low voltage on the FET drain (about +3 Volts).
Any idea on you side on how to do that ?
Cheers
Julien

[mmagin]

If you shorted the fet input, would that cause any harm?   If no to both questions, consider shorting the input to the fet with a normally-closed relay with a coil that runs off the low voltage supply.

Alternately, can you just prevent the high voltage from going on until the low voltage is on?  If it's a line voltage powered high voltage supply, maybe just use an ordinary relay (or SSR) to switch it on and off.  If you need to switch the high voltage itself, it looks like you're looking at fancy reed relays ($30+).