High Impedance Load Driving with Mosfet as Common Source Configuration

Thread Starter


Joined May 16, 2018
Hi all,
I am just trying a design ac switch with mosfets which are connected as common source. Mosfets will drive 16.2A load in normal conditions. When I try to drive 10 ohm load with 162V (peak, 400hz), as you can see in picture 1, there is no problem in load voltage. ( Green wave : Load Voltage, Red wave : Gate-Source Voltage)

I just try to increase load to 100k, I saw the almost 162V on load without gate firing. What is the reason of this ? Leakage current, drain-source parasitic capacitance etc.. and How can we handle this problem ? Is this really problem ? In addition, frequency is affecting the load voltage in off-state.
By the way, I saw the same thing on real circuit, not just a simulation.
I am waiting your kind comments,
Thank you,


Last edited:


Joined Apr 7, 2016
I can't answer exactly what happens in the simulation.

But with 1nF and 400Hz, I get an impedance of ~ 400KΩ, so D/S capacity is not insignificant.