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  4. For a zener regulated power supply, a zener diode with zener voltage Vz=6.0 V is used for regulation. The load current is to be 4.0 mA and the unregulated input 10.0 V. The value of series resistor Rs must be, it IZ / I2=5

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Q. For a zener regulated power supply, a zener diode with zener voltage $V_{z}=6.0\, V$ is used for regulation. The load current is to be $4.0 \,mA$ and the unregulated input $10.0 \,V$. The value of series resistor $R_{s}$ must be, it $I_{Z} / I_{2}=5$Physics Question Image

Semiconductor Electronics: Materials Devices and Simple Circuits

Solution:

The value of $R_{s}$ should be such that the current through the Zener diode is much larger than the load current. This is to have good load regulation. $I_{z}=20\, mA$.
The total current through $R_{s}$ is, therefore, $24 \,mA$.
The voltage drop across $R_{s}$ is $10.0-6.0=4.0\, V$.
This gives $R_{s}=4.0\, V /\left(24 \times 10^{-3}\right) A =167\, \Omega$