Semiconductor Diodes: Calculating Rf and Why VD=0

[Ghassan99]

Semiconductor dioedes !

when proving that the ideal diode is short circuit in forward biasing we calculate the diode Resistance Rf which is equal to the diode forward voltage upon it's forward current ...but why we put VD=0 why?

 

[vk6kro]

These are two different things.

An ideal diode is one that nobody has invented yet, but we assume we have one just to make the other calculations easier. If you are using a diode to rectify 30 volts AC then a voltage drop of 0.6 volts may be a trivial error which can be ignored.

If we don't want to regard the diode as ideal, then we can measure the forward voltages in the way you described.

 

[Ghassan99]

Thank you :)