I work in the R&D department for an electrolytic capacitor company. I have been asked to develop a completely automated data logging system using an Agilent aquasition unit.
I have to measure 8 high voltage capacitors simultaneously, these capacitors will be measured for internal pressure via a pressure transducer, internal temperature vie a thermocouple and leakage current, they will be kept in an oven a 95 degrees for the duration of the test. The capacitors are supplied 500vdc using a GENH750w power supply, they will be under test conditions for weeks even months. The capacitors may reach 70psi at different rates therefore I need to turn off the supply to those particular capacitors individually.


So, I have 8 outputs from a labjack U3 that go high when then the capacitors reach 70 psi, the labjack is powered by a USB. The idea in my head is to use the output to some how switch a Transistor,MOSFET,N Channel,SPP02N60S5 to turn on and off the supply to each individual capacitor, possibly using an opt isolator. I am thinking that I need to lower the 500vdc to something that can safely supply the gate of the mosfet.

Please, please can someone offer some suggestions?

Thanks

John

 

Sounds like you're using the N-channel on the high side. If that's so, try this:



When signal from driver goes low, Q1 stops conducting. D1 is a 12V Zener to keep the gate-to-source voltage of Q2 from getting out of hand. Note you'll need to float a second power supply on top of your 500Vdc.

I've had success with this trick in a 170Vdc H-bridge, as long as switching frequency stays relatively low.

 

You could use a single isolated 10V and eight optos to drive the gates of
eight 500V P-channel FET.

Another idea is the photovoltaic gate drive ICs from IR -- PVI1050, PVI5050, etc.
Be careful of these devices since they provide small gate drive currents. Your
power MOSFET will take longer to turn-on. You could use an N-channel device
with these drivers.

(* jcl *)