I want to confirm this circuit is going to work and ask how to calculate the zener voltage. The load is going to be driven by 30 volts, and the gate voltage is the same 30v, through an optocoupler.
closed as unclear what you're asking by Elliot Alderson, Mitu Raj, Finbarr, Kevin Reid, laptop2d Mar 7 at 2:43
Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.
On your schematic the 10k resistor (R1) is not placed correctly. It must be in series with the zener cathode. Then there is another resistor to ground (R2) to make sure the gate is at 0V when the input to gate is off. The value can be between 100k, sometimes even less, and 1M.
The zener must be rated 15V (or somewhere between 10 and 15V) to reduce the voltage to under 20V. The 10k resistor prevent too much current flowing through the zener and just enough for the mosfet gate.