What is a Zener diode and how does it work?
Characteristics of Zener Diode
The Z diode has a V(I) characteristic curve which is similar to letter "Z". Unlike "normal" rectifier diodes, the Z-diode is operated in the reverse-bias range. When a certain breakdown voltage is reached, the Zener effect and the avalanche effect take place, in which the current increases suddenly without destroying the Z diode. In the forward direction, the Z diode works like a normal diode.
Symbol and Characteristic Curve of Zener Diode
Zener Diode as a Voltage Regulator
Zener diodes are mainly used as a voltage regulator to maintain a constant DC output voltage. The following circuit converts unregulated input voltage VIn to a regulated output voltage VOut since the Zener voltage Vz and the output-regulated voltage VOut across the load are the same. The series resistor R1 serves to limit the diode current to IZ(max):
Zener Diode as a Voltage Regulator - circuit
Data sheet Zener Diode
Data sheet Zener Diode Exercise
Note: If, as here, the minimum Z current is not specified in the data sheet, the following rule of thumb applies:
. IZ(min) = 0.1 IZ(max)
Exercise
The following circuit is given. The measured values are as follows: VIN varies between 29 and 32 V. The load current varies between 5 mA and 22 mA. The Zener voltage can be assumed to be constant.
Zener Diode as a Voltage Regulator -circuit
Calculate the resistor R1 and select it from the E12 series.
- For what power must this resistor be designed?
- What are the effects if this resistor is rated too small or too large?
