4.66 It is required to design a zener shunt regulator to provide a regulated voltage of about 10 V.The available 10-V, 1-Wzener of type 1N4740 is specified to have a 10-V drop at a test current of 25 mA. At this current, its r z is 7 . The raw supply, V S , available has a nominal value of 20 V but can vary by as much as ±25%. The regulator is required to supply a load current of 0 mA to 20 mA. Design for a minimum zener current of 5 mA. (a) Find V Z0 . (b) Calculate the required value of R. (c) Find the line regulation. What is the change in V O expressed as a percentage, corresponding to the ±25% change in V S ? (d) Find the load regulation. By what percentage does V O change from the no-load to the full-load condition? (e) What is the maximum current that the zener in your design is required to conduct? What is the zener power dissipation under this condition?

4.64 Provide two designs of shunt regulators utilizing the 1N5235 zener diode,which is specified as follows: V Z =6.8 V and r z = 5 for I Z = 20 mA; at I Z = 0.25 mA (nearer the knee), r z = 750 . For both designs, the supply voltage is nominally 9 V and varies by ±1 V. For the first design, assume that the availability of supply current is not a problem, and thus operate the diode at 20 mA. For the second design, assume that the current from the raw supply is limited, and therefore you are forced to operate the diode at 0.25 mA. For the purpose of these initial designs, assume no load. For each design find the value of R and the line regulation.

4.63 Design a 7.5-V zener regulator circuit using a 7.5-V zener specified at 10 mA. The zener has an incremental resistance r z = 30 and a knee current of 0.5 mA. The regulator operates from a 10-V supply and has a 1.5-k load. What is the value of R you have chosen?What is the regulator output voltage when the supply is 10% high? Is 10% low? What is the output voltage when both the supply is 10% high and the load is removed? What is the smallest possible load resistor that can be used while the zener operates at a current no lower than the knee current while the supply is 10% low? What is the load voltage in this case?