Temperature Coefficient

3.3 Temperature Coefficient

The Zener voltage of a Zener diode is affected by temperature. The temperature coefficient (α) quantifies this relationship and is defined asα=VZ1ΔTΔVZ, whereΔVZis the change in Zener voltage for a change in temperature

ΔT

. Zener diode with Zener voltages below approximately 4 - 5V usually have a negative temperature coefficient, meaning the Zener voltage decreases as the temperature rises. Conversely, Zener diodes with Zener voltages above about 6V typically have a positive temperature coefficient. At around 5 - 6V, the temperature coefficient can be close to zero, making these Zener diodes more suitable for applications where temperature - stability of the regulated voltage is required.

4. Applications

4.1 Voltage Regulation

One of the most common and important applications of Zener diode is in voltage - regulation circuits. In a simple voltage - regulator circuit, a Zener diode is connected in parallel with the load, and a series - current - limiting resistor is placed between the power supply and the parallel combination. When the input voltage fluctuates or the load current changes, the Zener diode maintains a relatively constant voltage across the load. For example, in a battery - powered device, as the battery voltage gradually decreases during use, the Zener diode can ensure that the voltage supplied to the circuit remains stable within a certain range.

4.2 Voltage Reference

Zener diode are widely used as voltage references in electronic systems. In precision analog circuits, such as analog - to - digital converters (ADCs) and digital - to - analog converters (DACs), a stable and accurate voltage reference is essential. By carefully selecting a Zener diode with a precise Zener voltage and using appropriate compensation techniques, a reliable voltage reference can be established. This voltage reference provides a standard voltage level for comparison and calibration in various electronic circuits.

4.3 Over - Voltage Protection

Zener diode also serve as effective over - voltage protection devices. In power - supply circuits, sudden voltage spikes or surges can occur due to external factors like lightning strikes or internal factors such as the switching of inductive loads. These voltage surges can damage sensitive electronic components. A Zener diode connected across the power - supply lines or in parallel with the component to be protected will conduct when the voltage exceeds its Zener voltage, diverting the excess current and protecting the component from over - voltage damage.