Zener diodes (Zener diodes) achieve voltage stability and protection functions in circuits through their reverse breakdown characteristics. Their core role can be analyzed from the following four dimensions:
1. Voltage clamping and voltage stabilization protection
Core function: When the reverse voltage reaches the stabilized value (Vz), the diode enters the breakdown region, causing a sharp increase in current while the voltage remains almost unchanged, forming a voltage clamping effect.
Application scenarios:
Power circuit: Connect current limiting resistors in series and parallel to both ends of the load to provide stable voltage for chips, sensors, etc. For example, by paralleling a 6.2V voltage regulator diode in a 5V power supply, the output voltage can be stabilized at 6.2V.
Calculation example: If the load current is 20mA, the current limiting resistor R=(V_in - Vz)/Iz needs to be selected. Assuming the input voltage is 12V, R=(12-6.2)/0.02=290 Ω. In practice, standard resistors of 270 Ω or 300 Ω can be selected.
2. Overvoltage protection and surge absorption
Protection mechanism: When a transient high voltage (such as lightning strikes or power fluctuations) occurs in the circuit, the voltage regulator diode will first break down and conduct, limiting the voltage to a safe range and avoiding damage to the subsequent components.
Typical applications:
Communication interface protection: Parallel voltage regulator diodes are connected to RS-485 and CAN bus data ports to suppress ESD electrostatic discharge or lightning surge.
Parameter selection: The model with Vz slightly higher than the normal operating voltage should be selected based on the overvoltage amplitude, while ensuring that Izmax is greater than the peak surge current.
3. Voltage reference and precision reference
Characteristic utilization: Low temperature coefficient (TC) voltage regulator diode (such as 1N829 series, TC=± 0.01%/℃) can provide high-precision voltage reference.
Application case:
ADC/DAC circuit: As a reference voltage source, its stability directly affects the accuracy of analog-to-digital conversion.
Temperature compensation: Combined with a thermistor, a zero temperature coefficient reference voltage is constructed for high-precision measurement equipment.
4. Waveform modification and signal processing
Nonlinear application: Utilizing the breakdown characteristics of voltage regulators to limit, clip, or shape AC or pulse signals.
Typical scenario:
Audio circuit: Parallel voltage regulator diodes are connected in the audio signal to limit the maximum amplitude and prevent speaker overload.
Digital circuit: Clipping sine waves into square waves as clock signals or trigger pulses.
The correlation between selection parameters and their effects
Dynamic resistance (Rz): The smaller Rz, the higher the voltage clamping accuracy, making it suitable for precision voltage stabilization scenarios.
Temperature coefficient (TC): TC affects the long-term stability of the reference voltage, and the appropriate level should be selected based on the ambient temperature.
Package power consumption (Pz): High current voltage regulation requires the selection of high Pz devices or the installation of heat sinks to avoid thermal failure.
summarize
Zener diodes are widely used in power management, communication protection, precision measurement, and other fields due to their four core functions of voltage clamping, overvoltage protection, reference provision, and signal processing. When selecting, it is necessary to comprehensively evaluate parameters such as Vz, Izmax, Rz, TC, etc., to ensure that they match the circuit requirements and achieve efficient and reliable circuit protection and voltage regulation functions.
