Topic: Analog Circuits
A 24 V, 600 mW Zener is to be used for providing a 24 V stabilized supply to a variable load. Assume that for proper Zener action, a minimum of 10 mA must flow through the Zener. If the input voltage is 32 V, what would be the value of R and the maximum load current?
- A. 320 ohm, 10 mA
- B. 400 ohm, 15 mA
- C. 400 ohm, 10 mA
- D. 320 ohm, 15 mA
Answer: D. 320 ohm, 15 mA
Explanation: When $V_{z}=24V$, $P_{z}=600~mW$, $I_{zk}=10~mA$. $I_{zmax}=\frac{P_{zmax}}{V_{z}}=\frac{600~mW}{24~V}=25~mA$. When $I_{zmax}$ occurs, no current flows through $R_{L}$ i.e. $R_{L}$ is open circuited. $25~mA=\frac{32-24}{R} \Rightarrow R=\frac{8~V}{25mA}=320~\Omega$. Current from source $I=\frac{32-24}{320}=25mA$. Maximum load current $I_{Lmax}=I-I_{zk} = 25~mA-10~mA=15~mA$.