Some little knowledge about switching power supply
A switch mode or switched mode power supply or SMPS is a power supply unit (PSU) that uses some sort of switching device to transfer power from a source to a load. Usually the source is AC or DC and the load is DC. A common application is a power supply unit for a computer. Switch mode power supply (SMPS) has become a standard power supply unit for electronic equipment due to its high power density. A power supply unit is an important part of a circuit as it provides power to the circuit in order to function properly. Electronic devices require a constant voltage without fluctuations. The power supply will take uncontrolled power and convert it into a stable regulated power supply. There are basically two types of power supplies: linear regulated power supplies and switched mode power supplies (SMPS).
A linear regulated power supply is a power supply whose output voltage can be adjusted by series control elements. A basic example of a series transfer element is a resistor. But commonly used series transfer elements are BJTs or MOSFETs in active or linear mode, in series with the load. According to the change of input or load, the current of the transistor will change to maintain a constant output of the switching power supply. The difference between input and output (load) voltage is reduced across the transistor, and the difference between input and output (load) power is dissipated by the transistor as heat. The incoming AC power is supplied to a rectifier and filter to convert it to DC. But this DC source is not controlled because it can easily vary with changes in the input. This unregulated DC supply serves as the input to the linear regulator.
