A semiconductor diode blocks current in the opposite direction, but will fail prematurely if the reverse voltage applied across the terminals becomes too high. However, Zener diodes or "breakdown diodes" as they are sometimes called, are essentially the same as standard PN junction diodes, but specially designed to have a specified low reverse breakdown voltage taking advantage of any reverse voltage is applied. to her. The Zener diode works like a regular general purpose diode made of PN silicon junction and when it is forward biased. That is, anode to its cathode it behaves like a normal signal diode carry rated current. However, unlike a conventional diode which blocks all current flowing through itself when reverse biased i.e. cathode becomes more positive than anode, as soon as reverse voltage reaches a predetermined value, Zener diode start to lead in the opposite direction. This is because when the reverse voltage applied across the Zener diode exceeds the rated volta