Voltage regulator is a device which provides a constant and regulated voltage at the output, irrespective of the variations in the supply voltage. Zener diode is used as a regulator in the electronics circuits in reverse voltage. Its this property to regulate voltage is due to its characterstics.

　　We can see that after a certain voltage in the reverse voltage, the voltage across the diode remains constant for large variations in the current, which is called regulation. Below is the circuit of zener as a voltage regulator.

　　There is a certain value of voltage V and resistance R at which the diode operates in the breakdown region. The value of the voltage and resistance is so that the diode in the breakdown region. In the circuit the zener voltage Vz is also the voltage across the load Rl.

　　Now let us study that how the diode regulates the voltage at these conditions. The diode regulates the voltage across the load because in the breakdown region, large variations in diode current produces only small(almost constant) variations in the diode voltage, as the graph in the characterstics. is almost constant in the breakdown region. So in this way the diode regulates the voltage.

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