# PN Junction Diode

#### s.kaushik

Joined Apr 10, 2007
2
when will be the notes on PN junction diode be updated ... also the formula of the current flowing through a diode is really confusing...
Actually when the input voltage is around 5V at room temperature ..the current I comes out to be around 10^72amps which seems absurd ... please explain

#### Papabravo

Joined Feb 24, 2006
20,624
The explanation is simple. You can't get a forward voltage of 5V across a diode. Long before that happens, there will be enough current through the diode to produce enough heat to destroy the device. You can get some idea of the maximum voltage you could ever measure across the device by putting in some value of current larger than the absolute maximum rating from the datasheet and solving for the voltage.

In fact it would be a good exercise in algebra to rearrange the equation to express forward voltage as a function of current. You should expect large changes in current to produce very tiny changes in forward voltage, because the inverse of an exponential function is a log function.