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Zener diode structure and working principle - Database & Sql Blog Articles
The Zener diode shares a similar basic structure with a regular diode, as it is also a PN junction. However, due to specific manufacturing techniques, the PN junction can withstand reverse breakdown without being damaged. This unique property allows the Zener diode to be used for voltage regulation. When the reverse voltage reaches a certain threshold, a significant reverse current flows through the device while the voltage remains nearly constant. This phenomenon is known as Zener breakdown and the stable voltage at this point is referred to as the Zener voltage.
For silicon Zener diodes with a regulated voltage below 5V, the operation is primarily based on the Zener breakdown mechanism. In contrast, when the reverse voltage is higher, the breakdown occurs due to an intense electric field, leading to what is called avalanche breakdown. The resulting stable voltage in this case is known as the avalanche voltage, and it is typically observed in Zener diodes with a rated voltage above 7V.
The U-I characteristic curve of a Zener diode illustrates its voltage regulation behavior. As shown in the graph, the curve resembles that of a standard diode in the first quadrant, where the diode conducts in the forward direction. However, in the third quadrant, when the reverse voltage increases to the Zener voltage (UZ), the current rises sharply while the voltage remains almost constant. This region is where the Zener diode operates for voltage stabilization.
It’s important to note that the Zener diode must not exceed its maximum allowable current during reverse bias, or it may get damaged. Therefore, proper current limiting is essential when using Zener diodes in voltage regulator circuits.
In temperature-sensitive applications, a special type of Zener diode is used, which incorporates temperature compensation. This design involves two Zener diodes connected in such a way that one operates in the forward direction and the other in the reverse. Due to the opposite temperature coefficients of their voltage drops, the combined effect cancels out temperature-induced variations, ensuring more stable output voltage.
Finally, the current direction in a Zener diode differs from that of a regular diode. While a normal diode allows current to flow from the anode to the cathode, a Zener diode conducts in the reverse direction, with current flowing from the cathode to the anode when it is in the breakdown region. This makes it suitable for voltage regulation applications.