Zener Diodes

by the special sehematic symbol, shown within the basic cireuit diagram of the above figure. To make a DC voltage regulator, the Zener diode is connected in reverse bias. Its anode is connected to circuit common and its eathode is conneeted through a series resistanee to the positive terminal of the power source. The resistanee of the Zener diode will vary during circuit operation. It attempts to maintain a constant voltage across its terminals under varying current conditions in the cireuit. In this manner it acts as a voltage regulator. The Zener diode is placed in parallel with the load. When the load resistance decreases, the Zener diode´s internal resistanee will inerease. This will restore the voltage to its original value. When the load resistanee inereases, the Zener resistanee will deerease. This also restores the output voltage to its original value.

 

Zener diodes Characteristic

 

 

 

lt is just like an ordinary silicon diode. In the leakage region (between zero and breakdown), it has only a small leakage or reverse current through Zener diode, the breakdown has a very sharp knee, followed by an almost vertical inerease in current. Note that voltage is almost constant. Approximately it equals Vz over most of the breakdown region.