Question

The zener voltage of a zener diode is kept at a desired value by (A) adjustment the input voltage (B) adjustment the input current (C) by connecting an appropriate resistance in series (D) changing the level of doping

Short answer

The correct method to maintain the zener voltage at a desired value is by connecting an appropriate resistance in series with the zener diode. This ensures that the zener diode operates in its breakdown region, where the zener voltage is maintained at the desired value. The correct answer is (C).

Step-by-step solution

Option A: Adjust the input voltage

Adjusting the input voltage can change the voltage across the zener diode. However, if the input voltage is too low, the zener diode will not work in its breakdown region, and the zener voltage will not be maintained. Therefore, this option is not the correct way to keep the zener voltage at the desired value.

Option B: Adjust the input current

Adjusting the input current can also change the voltage across the zener diode. However, this can also lead to the zener diode to work outside its breakdown region, and the zener voltage will not be maintained. Therefore, this option is not the correct way to keep the zener voltage at the desired value.

Option C: Connect an appropriate resistance in series

By connecting an appropriate resistance in series with the zener diode and adjusting its value, we can ensure that the zener diode operates in its breakdown region. This is where the zener voltage is maintained at the desired value. Therefore, this option is the correct way to keep the zener voltage at the desired value.

Option D: Changing the level of doping

Changing the level of doping can change the zener voltage, but it is not a practical method. Once the zener diode has been fabricated with a specific doping level, it can't be easily modified externally. Hence, this option is not the correct way to keep the zener voltage at the desired value. So, based on our analysis, we can conclude that the correct answer is: (C) by connecting an appropriate resistance in series.