An alternative to open loop control is feedback control wherein the input voltage E is adjusted continually based on the measured current (feedback). For example let us assume that the controller behaves as per the following law:

We assume that the current measurement is available without any delay. The resulting differential equation can be re-written as follows:

The response of the current if the controller comes into action at time t=0, and when initial current is zero is:

In steady state, . However, if K is very large compared to R, then in steady state (approximately), . This will also ensure that response will be faster and practically independent of R.

In practice K cannot be made too large, because it is possible that some component of transient response due to the unmodelled measurement (sensor) block may get destabilized.

The controller described above is called a proportional controller. An alternative to having large K to obtain , is to modify the nature of the controller. We can also use an integral controller for performing regulation function.