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Explain the use of Zener diode as a voltage regulator. |
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Answer» SOLUTION :When the ac input voltage of a rectifier fluctuates, its rectified output also fluctuates. To get a constant dc voltage from the dc unregulated output of a rectifier a zener diode can be used. The circuit diagram of a dc voltage regulatorusing a zener diode is shown in figure.  The unregulated dc voltage (filtered output of a rectifier) is connectedto the zener diode which through a series resistance `R_(S)` such that the zener diode is REVERSE biased. If the input voltage increases, the current through `R_(S)` and zener diode also increases. This increases the voltagedrop across `R_(S)` without any change in the vltage across the zener diode. This is because in the breakdown region, zener voltage REMAINSCONSTANT even though the current through the zener diode changes. Similarly, if the inputvoltage DECREASES the current through `R_(S)` and zener diode also decreases. The voltage drop across `R_(S)` decreaseswithout any change in the voltage across the zener diode. Thus, any increase\decrease in the inputvoltage results in increase\decrease of the voltage drop across `R_(S)` without any change in voltage across the zener diode. Thus, the zener diode acts as a change in voltage across the zener diode we have to select thezener diode according to the required output voltage and ACCORDINGLY the series rresistance `R_(S)`. |
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