Voltage regulator IC in Mobile Phone
A voltage regulator is designed to automatically maintain a constant voltage level.
A voltage regulator may be a simple "feed-forward" design or may include negative feedback control loops. It may use an electromechanical mechanism, or electronic components.
Electronic voltage regulators are found in devices such as computer & Mobile Phone, power supplies where they stabilize the DC voltages used by the processor and other elements.
Electronic voltage regulators
A simple voltage/current regulator can be made from a resistor in series with a diode (or series of diodes)