Which are the current equations used when negative Drain-Source Voltage is applied to a N-Channel MOSFET (SimElectronics)?

I am currently using the elec_mosfet simulink example in order to investigate the behavior of the n-channel MOSFET model under reverse Drain-Source bias when Vgs=0. When the parameters are set: Vds_min=0, Vds_max=5, t_sim=10, Vgs=0 (Positive Drain-Source Bias) no current flows through the MOSFET as expected. However when the parameters are set: Vds_min=0, Vds_max=-5, t_sim=10, Vgs=0(Negative Drain-Source Bias) substantial current flows through the MOSFET (Approximately -27A for Vds=-5V). This phenomenon is not explained by the Simulink Documentation of the component. The same apply for the SPICE compatible LEVEL-1 MOSFET. Why does this happen? I would expect the Ids-Vds curves of the N-Channel MOSFET to be symmetrical (for positive-negative Drain-Source Bias) if the in built diodes are neglected. Is there a way to fix this?

[Mohsen Aleenejad]

Could you please attach your model so I can duplicate the issue on my side?

Answer 1

[Sabin]

In contrast to the IGBT, the MOSFET can conduct from the source to the drain when the source potential is higher. In analog applications for example, the MOSFETs have symmetrical physical structure for drain and source. Therefore, these terminals can be interchanged while keeping the same functionality.

The result is as expected. In the first case the Vgs = 0 < Vthreshold and the MOSFET is OFF. In the second case we have Vgd = 5 > Vthreshold and therefore the MOSFET will turn ON.