Figure 1. I-V curve of a diode. Source. This image shows well how the diode is only an approximation of the ideal one way device. Notably, there is this Vd non-ideal voltage drop across the device, which can be modelled as constant. It is however an exponential in fact.Video 1. Diodes Explained by The Engineering Mindset (2020) Source. Good video:
Ciro Santilli 
