LT Simulation Help Needed

Thread Starter


Joined Jan 17, 2016
Hey Guys,

I was simulating circuit to meet below requirement.
Vin<18V, Vout=0V
18V>Vin<30V, Vout=Vin

Simulation it works in ltspice but i see problem about VGS of MOSFET follow the input voltage and hence it can damage the mosfet.
I tried adding zener in the gate of MOSFET but it did not work as expected. Also if make opamp supply using zener even same problem i see.

Can anyone help me here .
How to reduce VGS value.
No other power supply will be used and we have to use input voltage eg. 5V to 30V.

Thanks in Advance !
Last edited:


Joined Mar 14, 2008
You can also add a resistor between the source and gate.
This will reduce the Vgs by the ratio of that resistor and the gate resistor to U1 out.
For example, if the two resistors are equal then the maximum Vgs would be 1/2 the supply voltage or 9V for an 18V supply.