How to Calculate Mosfet Voltages


For a N-channel Mosfet does Vds = Vdb + Vbs? Is this only true for simple models or always?

Where d is drain, s is source and b is base.

Best Answer

B is body on a MOSFET, not base. The relation you posted is true regardless of model - it's how the pin voltages are defined.

The voltages of the source, drain, gate, and body pins are Vs, Vd, Vg, and Vb. However, the absolute voltages are not important - the differences are. So the differences are defined as Vgs = Vg - Vs, Vds = Vd - Vs, Vgb = Vg - Vb, etc.

Following this convention, Vdb = Vd - Vb and Vbs = Vb - Vs so Vds = Vd - Vb + Vb - Vs = Vd - Vs.