MOSFET / BJT Leakage Current

[siegmar]

mosfet leakage current

Hello people
I have a small problem and maybe somebody has a better solution.
A 15 nF capacitor is charged on 450 V.
The capacitor should be discharged over a resistor of 4.7 Mohm in 100 µs impulses.
Unfortunately, the Drain to Source Leakage Current of the body diode of the MOSFET's is too high !!
Is a high voltage BJT transistor a better solution or I have simular problems with Leakage current? I can found nothing about this Leakage Current in the data sheet's.
Maybe the High Voltage transistor FMMT 459 is the right part ? The Vce (sat) is only 70mV, but nothing is written about the Leakage Current or I am blindly.
I have to order some samples for testing. But maybe I am wrong and a better solution is possible.
IGBT without a Body Diode ?
Another solution is maybe an HV relay. But I found only relay with a 1 ms switch time.
Are faster relay's on the market ?
Thanks in advance and have a nice day !
With best of all regards
Siegmar

 

[FvM]

bjt leakage current

Do you mean, that want to switch-on the discharge through the 4.7Mohm resistor for 100 µs intervals? This may be complicated due to the switch transistor output capacitance, it may be more easy to operate the transistor as a current source.

I see a cutoff-current specification in FMMT459 datasheet however. There are also small signal MOSFET with similar low cutoff-currents, e.g. BSS127. You didn't give a specification, so I don't know if they fit. Mechanical relays have generally switching times in a ms order of magnitude, and they mostly have contact bounce in addition, except for mercury wetted contacts. Finally, I'm not aware of small-signal IGBT, that can be expected to have low leakage currents.