Zener
1. Zener Overview
Zener diode (also known as voltage regulator diode) is a semiconductor device that uses the characteristic that the current changes greatly while the voltage remains stable during the reverse breakdown of the PN junction to achieve the voltage regulation function. Its core characteristic is that the reverse resistance near the critical reverse breakdown voltage (Vz) decreases sharply, so that the voltage is stabilized within a specific range.
2. How do Zeners Work?
1) Reverse breakdown mechanism:
Zener Breakdown: Occurs in highly doped PN junctions, directly destroys covalent bonds through strong electric fields, and the current increases sharply, with a negative temperature coefficient.
Avalanche Breakdown: Occurs in low-doped PN junctions, carriers trigger avalanche effects through collision ionization, and have a positive temperature coefficient.
2) Volt-ampere Characteristics:
The forward characteristics are similar to those of ordinary diodes; in the reverse breakdown region (voltage regulation region), the voltage is almost unchanged (Vz value), and the current can vary over a large range.
3. What are the Key Parameters of Zeners?
Breakdown Voltage (Vz): core indicator, determines the voltage regulation value, ranging from 2.4V to more than 200V.
Stable Current (Iz): includes the minimum voltage regulation current (Izk) and the maximum allowable current (Izm), which needs to be designed between the two to ensure stable operation.
Power Consumption (Pz): determined by the package form (such as DO-41 package can reach 1W), and must meet Vz×Iz≤Pz to avoid overheating.
4. What are Zeners Used for?
Voltage Regulation Circuit: provides a stable voltage reference for the load, such as the MCU power clamp (5.1V or 3.3V).
Overvoltage Protection: used to suppress transient high voltage or surge (such as multiple Zeners in parallel to share current in TVS applications).
Voltage Reference Source: used as a reference voltage component in precision circuits.
5. Precautions for Using Zeners
Series Configuration: When used to increase the total voltage regulation value, it is necessary to select matching, control temperature consistency, and add balancing resistors to prevent uneven voltage.
Parallel Configuration: Strict matching parameters or series current limiting resistors are required to avoid the “domino failure” phenomenon.
Power Consumption Margin: A sufficient power margin must be reserved to prevent thermal breakdown.
6. Differences from Other Diodes
TVS Diode: Dedicated to transient overvoltage protection, fast response speed (sub-nanosecond level), and stronger surge absorption capacity.
Schottky Diode: It is known for its low forward voltage drop (0.3~0.5V) and high switching frequency, and is mainly used for high-frequency rectification.
Zener diodes have both voltage regulation and protection functions in electronic systems through precise breakdown voltage control and thermal management design. Its application needs to be combined with specific parameter selection and circuit configuration optimization to ensure reliability and stability.