There are maximum integrated IC’s that need a constant voltage with which they could operate. They have their voltage regulator no matter whether it is a simple Logic Gate or a complex microprocessor. The most common operating voltages are 5V, 12V, and 3.3V.To act as a voltage source we have batteries and DC Adaptors as the maximum time to our circuit design they cannot be directly connected since the voltage from them is not regulated.
A voltage regulator is a beefed-up emitter follower. A transistor a stable reference is connected that spits out a constant voltage, dropping the remaining.
They even consist of a built-in error amplifier, which samples the output voltage (again through a divider), then with the reference voltage it is compared, the difference is calculated, and accordingly drives the output transistor. From voltage divider, this is far different, which through just a magnitude smaller faithfully replicates the input signal.
