Diode

[sreedhar]

How is the Diode able to maintain current independent of voltage once after the cutin voltage is crossed in forward bias and also how zener effect works (where current is independent of voltage) in voltage regulators -how self adjusting property of zener works?

---------plz explain..

[vivo]

The diodes resistance varies with the current passing through it,when it reaches the set voltage 0.7v its resistance falls with increases in current and the voltage drop on the other resistance in the circuit increases with the increase in current.So when the supply voltage increases the volts drop across the diode increases but only slightly as compared to the drop of the other resistance in the circuit.Zenner diodes work in much the same way but the point at which the resistance fall effects the other parts of the circuit is set during manufacture.