ZENER DIODE AS VOLTAGE REGULATOR

Explanation

A Zener diode is a heavily doped pn-junction diode operated in its breakdown region.
Principle : In the breakdown region of a Zener diode, large change in the current can be produced by almost insignificant change in the reverse-bias voltage. In other words, for widely changing Zener current, the voltage across the Zener diode remains almost constant.

Electric circuit : The circuit for regulating or stabilizing the voltage across load resistance `R_(L)` against change in load curernt and supply voltage is shown in the figure. The series resistance R limits the current through the diode below the maximum reateed value.
Working : WHen the input unregulated dc voltage V across the Zener diode is greater (in magnitude) than the breakdown region. The voltage across the diode and the load `R_(L)` is then `V_(z)`. The corresponding current in the diode is `I_(z)`.
As the load current or supply voltage changes, the diode current adjusts itself at constant `V_(z)`. The excess voltage `V-V_(2)` appears across the series resistance R.
Since the voltage across `R_(L)` remains constants at `V_(z)`, The Zener diode acts as a voltage stabilizer or voltage regulator.