A Zener diode is a special kind of diode which permits current to flow in the forward direction as normal, but will also allow it to flow in the reverse direction when the voltage is above a certain value-the breakdown voltage known as the Zener voltage.
V-I Characteristics of the Zenor Diode:
• The illustration above shows this phenomenon in a current vs voltage graph with a zener diode connected in the forward direction .It behaves exactly as a standard diode.
• In the reverse direction however there is a very small leakage current between 0v and the zener voltage –i.e. just a tiny amount of current is able to flow.
• Then, when the voltage reaches the breakdown voltage(vz),suddenly current can flow freely through it.
Zenor Diode voltage regulator circuit
• Since the voltage dropped across a Zener diode is a known and fixed value,Zener diode are typically used to regulate the voltage in electric circuits.
• Using a resistor to ensure that the current passing through the Zener diode is atleast 5mA.
• The voltage drop across the diode is exactly equal to the Zener voltage of the diode.