1) Pulse width modulation type, referred to as Pulse Width Modulation (PulseWidthModulaTIon, abbreviated as PWM) type. Its main feature is that the switching frequency is fixed, and the duty cycle is adjusted by changing the pulse width to achieve the purpose of voltage regulation. At its core is a pulse width modulator. The fixed switching period provides convenience for designing the filter circuit. However, its disadvantage is that due to the limitation of the minimum on-time of the power switch, the output voltage cannot be adjusted in a wide range; in addition, the output terminal is generally connected to a dummy load (also known as a preload) to prevent the output voltage from rising at no-load. . At present, most of the integrated switching power supply adopts PWM method.
The efficiency of switching power supplies is much higher than that of linear power supplies. This saves energy, so it is favored by people. But it also has shortcomings, that is, the circuit is complicated, maintenance is difficult, and the pollution to the circuit is serious. The power supply is noisy and not suitable for some low-noise circuits. The technical pursuit and development trend of switching power supply can be summarized into the following five aspects:
1) Miniaturization, thinning, lightweight, and high frequency.
2) High reliability.
3) Low noise.
4) Adopt computer-aided design and control.
5) Low output voltage technology.
The development of switching power supply has always been closely related to the development of semiconductor devices and magnetic components. The realization of high frequency requires corresponding high-speed semiconductor devices and high-frequency electromagnetic components with excellent performance. Develop new high-speed devices such as power MOSFET and IGBT, develop low-loss magnetic materials for high frequency, improve the structure and design method of magnetic components, improve the dielectric constant of filter capacitors and reduce their equivalent series resistance, etc. Power miniaturization has always had a huge push.
