Question

In a Zener regulator, source voltage is 25 V, series resistance is of 200 ohm, load resistance is of 500 ohm and Vz = 5 V. Find the minimum Zener current.​

Answer 1

Explanation:

The resistor value R_{s}R

s

is 167 ohm.

Solution:

The load current when regulated perfectly must have value of series resistance as R in order that the Zener diode has larger current flow than load current.

The value of series resistance is calculated as follows,

Given: Zener Voltage, V_{z}V

z

= 6 V

I_{c}I

c

= 4 m A

Unregulated input = 10A

\begin{gathered}\begin{array}{l}{I_{z}=5 \times 4} \\ {I_{z}=20 \mathrm{m} A}\end{array}\end{gathered}

I

z

=5×4

I

z

=20mA

Now the total current is given by, I=I_{c}+I_{z}I=I

c

+I

z

I = 20 + 4 = 24 m A

Voltage drop across the series resistance = Unregulated – Regulated

V = 10 – 6

V = 4 v

Therefore, series resistance R=\frac{V}{I}R=

I

V

\begin{gathered}\begin{aligned} R &=\frac{4}{24} m A \\ R &=4 \times \frac{1000}{24} \end{aligned}\end{gathered}

R

R

=

24

4

mA

=4×

24

1000

R = 167 ohm.