Basic Electronics (3110016)

BE | Semester-1   Winter-2019 | 06-01-2020

Q2) (b) 

Why Zener diode can be used as voltage regulator? Explain Zener as voltage regulator with necessary diagram.

  • Zener diode is a silicon semiconductor with a p-n junction that is specifically designed to work in the reverse biased condition.
  • When forward biased, it behaves like a normal signal diode, but when the reverse voltage is applied to it, the voltage remains constant for a wide range of currents.
  • Due to this feature, it is used as a voltage regulator in D.C. circuit. The primary objective of the Zener diode as a voltage regulator is to maintain a constant voltage.
  • Let us say if Zener voltage of 5 V is used then, the voltage becomes constant at 5 V, and it does not change.
  • There is a series resistor connected to the circuit in order to limit the current into the diode. It is connected to the positive terminal of the D.C. It works in such a way the reverse-biased can also work in breakdown conditions.
  • We do not use ordinary junction diode because the low power rating diode can get damaged when we apply reverse bias above its breakdown voltage.
  • When the minimum input voltage and the maximum load current is applied, the Zener diode current should always be minimum.
  • Since the input voltage and the required output voltage is known, it is easier to choose a Zener diode with a voltage approximately equal to the load voltage, i.e. VZ = VL.
  • The value of the series resistor is written as RS = ( VZ - VL ) I L.
  • Current through the diode increases when the voltage across the diode tends to increase which results in the voltage drop across the resistor.
  • Similarly, the current through the diode decreases when the voltage across the diode tends to decrease. Here, the voltage drop across the resistor is very less, and the output voltage results normally.
 

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