The following diagram shows a Zener diode as a voltage regulator. The Zener diode is rated at $V_z = 5\text{ V}$ and the desired current in load is 5 mA. The unregulated voltage source can supply upto 25 V. Considering the Zener diode can withstand four times of the load current, the value of resistor $R_s$ (shown in circuit) should be ___________ $\Omega$. 
To solve this problem, we need to find the value of the series resistor \( R_s \) that will allow the Zener diode to regulate the voltage at the desired level. Let's go through the steps:
- The Zener diode is rated at \( V_z = 5 \, \text{V} \). This means that the voltage across the Zener diode will be maintained at 5 V.
- The desired load current \( I_L \) is 5 mA.
- The maximum unregulated input voltage \( V_{\text{in}} \) is 25 V.
- The Zener diode can withstand up to four times the load current, i.e., \( I_Z \leq 4 \times 5 \, \text{mA} = 20 \, \text{mA} \).
The current through the resistor \( R_s \), \( I_s \), must be the sum of the current through the Zener diode, \( I_Z \), and the load current, \( I_L \):
\(I_s = I_Z + I_L\)
Substituting the maximum \( I_Z = 20 \, \text{mA} \) and \( I_L = 5 \, \text{mA} \) gives:
\(I_s = 20 \, \text{mA} + 5 \, \text{mA} = 25 \, \text{mA}\)
Using Ohm's law, the voltage drop across \( R_s \) is:
\(V_{\text{drop}} = V_{\text{in}} - V_z = 25 \, \text{V} - 5 \, \text{V} = 20 \, \text{V}\)
Now, use Ohm’s law to find \( R_s \):
\(R_s = \frac{V_{\text{drop}}}{I_s} = \frac{20 \, \text{V}}{25 \times 10^{-3} \, \text{A}} = 800 \, \Omega\)
Therefore, the value of resistor \( R_s \) should be 800 Ω.
Similar Questions
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List - I
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Choose the correct answer from the options given below :
Important Questions from Modern Physics
- Two electrons are moving in orbits of two hydrogen like atoms with speeds $3 \times 10^5 \text{ m/s}$ and $2.5 \times 10^5 \text{ m/s}$ respectively. If the radii of these orbits are nearly same then the possible order of energy states are ______ respectively.
- Given below are two statements:
Statement I: For all elements, greater the mass of the nucleus, greater is the binding energy per nucleon.
Statement II: For all elements, nuclei with less binding energy per nucleon transforms to nuclei with greater binding energy per nucleon.
In the light of the above statements, choose the correct answer from the options given below - A voltage regulating circuit consisting of Zener diode, having break-down voltage of 10 V and maximum power dissipation of 0.4 W, is operated at 15 V. The approximate value of protective resistance in this circuit is ______ $\Omega$.
The binding energy for the following nuclear reactions are expressed in MeV.
${}_2\text{He}^3 + {}_0\text{n}^1 \rightarrow {}_2\text{He}^4 + 20 \text{ MeV}$
${}_2\text{He}^4 + {}_0\text{n}^1 \rightarrow {}_2\text{He}^5 - 0.9 \text{ MeV}$
If $\text{X}_3, \text{X}_4, \text{X}_5$ denote the stability of ${}_2\text{He}^3, {}_2\text{He}^4$ and ${}_2\text{He}^5$, respectively, then the correct order is :Identify the correct truth table of the given logic circuit.
