I am using PSpice to simulate the parasitic BJT of a power VD-MOSFET, which under certain conditions can be turned on and lead to the destruction of the cell.
I have designed a model that is working well enough, but it doesn't take into account the temperature rise because of the increased currents flowing through the cell. To achieve that, I have to add a resistor in parallel to the BJT (Rtc in the attached picture), whose value is changing throughout the simulation.
As I first step, I would like Rtc to be decreased exponentially with time.
Is there a way to establish and use a function like this in PSpice?
Best Answer
I remember publishing a model of a variable resistor in Power Electronics and Intelligent Motion, the US magazine, in 2005. The idea was to control an inductance, a capacitance and a resistance by a voltage. The variable resistance model using PSpice analog behavioral equations is here:
.subckt VARIRES 1 2 CTRL
R1 1 2 1E10
G1 1 2 Value = { V(1,2)/(V(CTRL)+1u) }
.ENDS
It follows this simple model
and here is a simple test circuit using IsSpice at that time:
The 1-u source is there to prevent a divide-by-zero event and improves convergence during the bias point calculation.