I need a fast reacting way of discharging a capacitor and I figure a simple depletion PMOS is what I need. The time at which the gate has to have a voltage to keep the depletion PMOS closed is not important. It's taken cared of by the rest of the circuit.
Problem is, as all you know, depletion PMOS are not being manufactured (not economical enough??). So what are similarly behaving devices, preferably having the same footprint.
There are extremely few situations where a depletion mode MOSFET is necessary or preferred. It is extremely unlikely that you happen to have an application where you need to use such a device.
There is no reason to think that a depletion mode device will be as fast reacting as alternative more modern components. If you want it to act as a switch then you will need to hold it off until it needs to be on, and there is no reason that off to on speed of depletion mode device is especially fast compared to alternatives
Achieving fast reacting" circuits is 'just a matter of design'.
If you describe your requirement (rather than an assumed solution) in detail we will be able to assist you with a good solution using readily available components.
What order of switching speed do you require? Please tell us as much as possible about your application.
