The simple circuit in the above image is a Zener Regulator which takes an input voltage and regulates to an output voltage based on the breakdown voltage of the Zener. The property of Zener is that the voltage of Zener under reverse bias remains constant until the current exceeds the Maximum Zener current. However, designers do take care that for a given input voltage, the series resistor is selected such that current is limited and Maximum Zener current is not exceeded.
While the above points are all known to advanced engineers, there are some points which the beginners need to understand regarding the usage of this circuit. In academics, it is thought that Zener diode is used as regulator and the above circuit might be given as an example. But they were not thought in detail whether Zener regulator can be used in all scenarios or only some scenarios. To understand such scenarios, let us know below points:
- Zener can be used as regulator for very low loads. To give a figure, anything beyond 100mA required for load could be dooms for this approach
- Even if the load current is less, if the load current is varying continuously, this approach cannot be used
- One of the major problem with Zener voltage is that it is not precise, there is max and min value. This meant, we cannot use this circuit for requirements where precise voltage is required, Zener regulator is not a choice
- In scenarios where reference voltage is to be generated and involving low load current (high impedance like opamp input), Zener regulator is a definite option
- Zener cannot provide good line and load regulation capabilities which is a big disadvantage. this can be understood from the V-I graph of the Zener diode
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