Design a 7.5-V zener regulator circuit using a 7.5-V zener specified at 10mA. The zener has an incremental resistance of rZ = 30 Ω and a knee current of 0.5 mA. The regulator operates from a 10-V supply and delivers a nominal current of 5 mA to the 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 largest load current that can be delivered 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?

The answer is given in the explanation.

Explanation:

The circuit is as indicated in the attached figure.

From the analytical description the zener voltage is given as

Here

Vzo is the voltage at which the slope of 1/rz intersects the voltage axis it is equal to knee voltage.

The equivalent model is shown in the attached figure.

From the above equation, Vzo is calculated as

Here Vz is given as 7.5 V

Iz is given as 10 mA

rz is given as 30 Ω

Thus the Vzo is given as

The value of I_L is given as 5 mA

Now the expression of current is as

Now the resistance is calculated as

So the value of resistance is 186.66 Ω.

Considering the supply voltage is increased by 10%

V is 10-10%*10=10+1=11 so the

Considering the supply voltage is decreased by 10%

V is 10-10%*10=10-1=9 so the

Now if the supply voltage is 10% high and the value of Load is removed i.e I=Iz only which is 10mA

so

Now the largest load current thus that the supply voltage is 10% low and the current of zener is knee current thus

The load voltage is 7.485 V

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