Suppose you need to design a clipper circuit to clip off the portions of an input voltage that fall above +5 V or below +2 V. Assume that diodes having a constant forward drop of 0.7 V are available. Ideal Zener diodes of any breakdown voltage required are available. Dc voltage sources of any value needed are available.

attached below

Explanation:

The required design for a clipper circuit is attached below

From the attached circuit  

It can be seen that the battery voltage needs to be high so that it will be in forward bias considering the assumption that the diodes have a constant forward drop of 0.7 V.

hence  4.3 has to be  >2.7

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