If an electrical energy source and an electrical consumer are directly connected to one another in an electrical circuit , then current adaptation is understood to mean the condition under which the maximum electrical current is determined. It is also understood to be an action through which the maximum current is achieved.

Equivalent circuit diagram of a linear current source (with consumer)

This adaptation is described by the ratio of the internal resistance of the source (or its output resistance ) and the load resistance of the sink (or input resistance of the consumer). When using a source in the form of a linear current source , the current adjustment is implemented when the portion of the generated current intensity is as large as possible and the portion is as small as possible. That requires ${\ displaystyle R _ {\ text {i}}}$ ${\ displaystyle R _ {\ text {V}}}$${\ displaystyle I _ {\ text {K}}}$${\ displaystyle R _ {\ text {V}}}$${\ displaystyle R _ {\ text {i}}}$

${\ displaystyle R _ {\ text {V}} \ ll R _ {\ text {i}}}$.

The efficiency of a current source can be specified as a function of the resistance ratio , unlike with a voltage source , by ${\ displaystyle R _ {\ text {V}} / R _ {\ text {i}}}$

${\ displaystyle \ eta _ {\ text {I}} = {\ frac {1} {1 + {\ frac {R _ {\ text {V}}} {R _ {\ text {i}}}}}}}}$.

It is greater, the better the inequality above is fulfilled, and is then close to 100%.

The fact that the load resistance is smaller ( lower ) than the internal resistance of the power source leads to the term underfitting . Mostly, but not consistently, it stands for and only says something about non-compliance with the performance adjustment . ${\ displaystyle R _ {\ text {V}}