You know that in order to get a regulated DC voltage, we connect a Zener diode across the output terminals of a rectifier. Draw a circuit diagram comprising a Zener diode, series resistor `(R_(s))` and a load resistor `(R_(L))`. Indicate the directions of currents `I_(z),I_(s)(I=, the current) and `I_(L)` passing through Zener diode `R_(s)` and `R_(L)`, respectively. Choose the correct option from the following:
(1) `I_(L)=I_(z)` (2) `I_(L)gtI_(z)` (3) `I_(L)ltI_(z)`.
How can we achieve the right option?
In such a circuit, if `V_(Z)=6.0V,I_(L)=4.0mA,I_(z)=20mA` and the unregulated input is 10V, calculate the value of series resistor to work satisfactorily.

Explanation

Option (3) `I_(L)ltI_(Z)` is correct by keeping the value of resistance more for voltage regulation.
Here, load resistance =`R_(L)`
`l_(L)=4mA=4xx10^(-3)A`
Zener current, `I_(z)=20mA=20xx10^(-3)A`
`V=10V,V_(Z)=6V`
According to the circuit diagram,
`I_(R)=I_(Z)+I_(L)`
`=4xx10^(-3)+20xx10^(-3)`
`=24xx10^(-3)A`
Resistance, `R=(V-V_(z))/(I_(R))`
`=(10-6)/(24xx10^(-3))`
`=(4xx10^(3))/(24)=0.1667xx10^(3)Omega`
`=166.7Omega`