Series voltage regulator
The block diagram of a discrete transistor type voltage regulator is given below. A control element is placed to collect the unregulated input which controls the magnitude of the input voltage and passes it to the output. The output voltage is then fedback to a sampling circuit and then compared with a reference voltage and sent back to the output.
Thus, if the output voltage tends to increase the comparator circuit provides a control signal to cause the control element to reduce the magnitude of the output voltage by passing it through the sampling circuit and comparing it, thereby maintaining a constant and steady output voltage.
Suppose the output voltage tends to decrease, the comparator circuit provides provides a control signal that causes the series control element to increase the magnitude of output voltage, thus maintaining the steadiness.