Switching power supply is a power supply device for AC and DC conversion. It switches the input voltage into a pulse signal at a high frequency through the switching action of the switching tube, and then converts it into a DC voltage output through a rectification and filtering circuit. Switching power supply has the characteristics of high efficiency, small size, light weight, and good stability.
The basic working principle of the switching power supply is to switch the input voltage into a high-frequency pulse signal through the switching action of the switching tube. This high-frequency pulse signal is transformed by a transformer or inductor and processed by a filter circuit, and finally a stable DC output voltage is obtained. The output voltage of the switching power supply can be adjusted and stabilized as needed to meet the power requirements of different devices. Switching power supplies have many advantages, including high efficiency, good stability, small size, light weight, and high reliability. It is widely used in electronic equipment, communication equipment, computer equipment, industrial control systems and other fields, and has become one of the common power supply types in modern electronic technology.
Switching power supplies can be classified according to different classification standards, the following are several common classification methods:
According to the type of input power supply, it is divided into: 1. AC-DC switching power supply: convert alternating current to direct current. 2. DC-DC switching power supply: Convert DC power to another DC voltage.
EBYTE OEM/ODM Wholesale and retail Low power 12W power supply module ac-dc
[Input voltage]：100~250V
[Output voltag]：12V
[Output current]：1000mA
[Output Power]：12W
[Size]：38.2*25.2*23mm
[Package]：DIP
[Feature]：12W low power AC-DC buck power supply module
[Introduction]：12W low power AC-DC buck power supply module
Classified by working mode: 1. Single-ended switching power supply: only one switching tube, suitable for low-power applications. 2. Double-terminal switching power supply: There are two switching tubes, which are suitable for high-power applications.
Classification by topology: According to topology, it can be roughly divided into Buck (step-down), Boost (boost), Buck-Boost (step-down-boost), Flyback (flyback), Forward (forward), Two-Transistor Forward (Double Transistor Forward), Push-Pull (Push-Pull), Half Bridge (Half Bridge), Full Bridge (Full Bridge), etc. These classification methods are only part of them. Switching power supplies can also be customized according to other specific requirements and applications. A more detailed classification.
Next, we will introduce the commonly used Flyback (flyback) and Forward (forward). Forward and flyback are two different switching power supply technologies. Forward switching power supply refers to the use of forward high-frequency transformer isolation coupling The energy switching power supply corresponds to the flyback switching power supply. The structure of the forward switching power supply is relatively complicated, but the output power is very high, suitable for 100W-300W switching power supply, generally used in low-voltage, high-current switching power supply, and widely used.
As shown in the figure below, the forward switching power supply specifically means that when the switching tube is turned on, the output transformer acts as a medium to directly couple the magnetic field energy, and the electric energy and magnetic energy are mutually converted, so that the input and output are performed simultaneously. There are also deficiencies in daily applications: if it is necessary to increase the back electromotive force winding (to prevent the back electromotive force generated by the primary coil of the transformer from breaking down the switch tube), an additional inductance is added to the secondary side for energy storage filtering, so compared with the flyback switching power supply. In other words, its cost is high, and the volume of the forward switching power supply transformer is larger than that of the flyback switching power supply transformer.
Forward switching power supply
As shown in the figure below, the flyback switching power supply refers to the switch electric excitation that uses the flyback high-frequency transformer to isolate the input and output circuits. Its transformer not only plays the role of transforming voltage and transmitting energy, but also plays the role of energy storage inductor. Therefore, the flyback transformer is similar to the design of the inductor. All circuits are relatively simple and easy to control, and the flyback type is widely used in the low power of 5W-100W. For the flyback switching power supply, when the switch tube is turned on, the inductance current on the primary side of the transformer rises. Since the output coil of the flyback circuit is opposite to the same name end, the output diode is cut off, the transformer stores energy, and the load is supplied with energy by the output capacitor. When the switch When the tube is cut off, the voltage induced by the inductance on the primary side of the transformer is reversed. At this time, the output diode is turned on, and the energy of the transformer supplies power to the load through the diode and charges the capacitor at the same time.
It can be seen from the comparison that the forward transformer only has the function of voltage transformation, and the whole can be regarded as a buck circuit with a transformer. The flyback transformer can be regarded as an inductor with voltage transformation function, which is a buck-boost circuit. Generally speaking, the working principle of forward and flyback is different. Forward is the primary work and the secondary also works. If the secondary does not work, there is freewheeling inductance, which is generally CCM mode. The power factor is generally not high, and the input and output are proportional to the variable ratio duty cycle. The flyback is the primary work, the secondary does not work, and the two sides are independent. Generally, in the DCM mode, the inductance of the transformer will be relatively small, and an air gap needs to be added, so it is generally suitable for small and medium power situations.
The forward transformer is ideal and does not store energy. However, since the excitation inductance is finite, the excitation current will make the magnetic core larger. In order to avoid magnetic flux saturation, the transformer needs the auxiliary winding to reset the magnetic flux. The working form of the flyback transformer can be regarded as a coupled inductor; the inductor first stores energy and then discharges energy. Since the input and output voltage polarities of the flyback transformer are opposite, when the switch tube is disconnected, the secondary can provide a reset voltage for the magnetic core. , so the flyback transformer does not need additional flux reset windings.
