Thevenin’s theorem is a simplification technique used in circuit analysis. Any complex network with several voltage sources & resistors can be reduced to a Thevenin's equivalent circuit consist of a single voltage source and a series resistance connected to a load.
But, the Thevenin’s theorem is not applicable for all circuits. This theorem has some limitations:
• A limitation of Thevenin’s theorem is that, it assumes that the circuit is completely linear. So, this theorem is applicable for resistors, but will not work well when trying to analyze circuits consisting of non-linear elements such as diodes.
• Actually, most of the circuits behaves like a linear circuit in a certain range of values, thus this theorem is valid only within this linear range.
• Thevenin’s theorem is applicable only for bilateral networks, that is, for those networks where current through an element is not affected with polarity changing.
• There should not be any magnetic coupling present in between the load & the network.
• The power dissipation by the Thevenin equivalent circuit is not always identical to the power dissipation by the real circuit. This particular limitation may lead disturbances in proper circuit analysis.