# Problem with stacked power mosfet simulation

I'm trying to build a Circuit Lab simulation of a stacked power mosfet pulser as described in this paper. The simulation runs for 10 ms. After 5ms, the switch flips and the voltage at 'StageOne' drops accordingly, however, the 'Output' does not drop. I think it's supposed to drop because the capacitor C1 keeps the gate slightly positive relative to the source of M2 which should result in M2 opening, however, I'm not an electronics engineer and I'm just guessing my intuitions around the operation of the circuit aren't certain. Can anyone please advise as to what I'm doing wrong?

simulate this circuit – Schematic created using CircuitLab

Your output is directly connected to the voltage source and therefore will never drop

• Looking at the paper, the resistor on the output of V1 is missing. In the paper's example, it was 51kΩ. There might be a default source resistance in CircuitLab, but it won't be anywhere near that.
– W5VO
Commented Mar 20, 2019 at 13:47

This circuit relies on M1 being off allowing C1 to charge to a certain voltage determined by R1/R2, in your circuit C1 should charge to 400 V DC.

Only after there is 400 V across C1, (you should check that in your simulation) then M1 can be switched on. That will pull down the source of M2 so M2 can start conducting. M2 will conduct as long as C1 has enough charge left to keep M2's gate voltage higher than its source voltage. So the pulse (time) that M1 is on should be short so that C1 cannot fully discharge.

This isn't an easy circuit so simulate when you're "just guessing" as it relies on some things being balanced properly (value of C1, C1 charge time, pulse width). Get it wrong and the circuit simply doesn't work. There is no need to be an electronics engineer as long as you understand how circuits and MOSFETs work.

• Thanks for your answer. I didn't mean the imply that I was guessing at the values to be used for the circuit. I meant that my understanding of the circuit operation wasn't certain. Commented Mar 22, 2019 at 2:53