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Brief introduction of switching power supply

Update:07-02-2021
Summary:

Switching power supply is a kind of power supply that u […]

Switching power supply is a kind of power supply that uses modern power electronics technology to control the time ratio of switching on and off to maintain a stable output voltage. Switching power supplies are generally composed of pulse width modulation (PWM) control ICs and MOSFETs. Compared with the linear power supply, the cost of the switching power supply increases with the increase of the output power, but the growth rate of the two is different. The cost of the linear power supply is higher than the switching power supply at a certain output power point, which is called the cost reversal point. With the development and innovation of power electronics technology, switching power supply technology is constantly innovating. This cost reversal point is increasingly moving to the low output power end, which provides a broad development space for switching power supplies.

High-frequency switching power supply is the direction of its development. High-frequency makes switching power supply miniaturized and enables switching power supply to enter a wider range of applications, especially in the application of new technology, which promotes the miniaturization and lightness of new technology products化. In addition, the development and application of switching power supplies are of great significance in saving energy, saving resources and protecting the environment.

Three conditions:

1. Switching: Power electronic devices work in a switching state instead of a linear state
2. High frequency: power electronic devices work at high frequency instead of low frequency close to power frequency
3. DC: The output of the switching power supply is DC instead of AC
Switching power supplies generally have three working modes: fixed frequency and pulse width mode, fixed frequency and variable pulse width mode, and variable frequency and pulse width mode. The former working mode is mostly used for DC/AC inverter power supply, or DC/DC voltage conversion; the latter two working modes are mostly used for switching regulated power supply. In addition, the output voltage of the switching power supply also has three working modes: direct output voltage mode, average output voltage mode, and amplitude output voltage mode. Similarly, the former working mode is mostly used for DC/AC inverter power supply, or DC/DC voltage conversion; the latter two working modes are mostly used for switching regulated power supply.

According to the way the switching devices are connected in the circuit, the more widely used switching power supplies can be roughly divided into three categories: series switching power supplies, parallel switching power supplies, and transformer switching power supplies. Among them, the transformer switching power supply (hereinafter referred to as the transformer switching power supply) can be further divided into: push-pull, half-bridge, full-bridge, etc.; according to the excitation of the transformer and the phase of the output voltage, it can be divided into: forward , Flyback, single and double excitation, etc.; if it is divided into use, it can be divided into more types.

Classification of switching power supply:

In the field of switching power supply technology, people are developing related power electronic devices and switching frequency conversion technology. The two promote each other to promote the switching power supply to light, small, thin, low noise, high reliability, with a growth rate of more than two digits every year. The direction of anti-interference development. Switching power supplies can be divided into two major categories: AC/DC and DC/DC. DC/DC converters have been modularized, and the design technology and production process have been mature and standardized at home and abroad, and have been recognized by users. The modularization of AC/DC, due to its own characteristics, makes it encounter more complicated technical and process manufacturing problems in the process of modularization. The structure and characteristics of the two types of switching power supplies are described below.

Grounded
Switching power supplies produce more interference than linear power supplies. Electrical equipment that is sensitive to common mode interference should take grounding and shielding measures. According to EMC restrictions such as ICE1000, EN61000, and FCC, switching power supplies adopt EMC electromagnetic compatibility measures, so switch Generally, the power supply should be equipped with EMC electromagnetic compatibility filter. For example, the HA series switching power supply of Lead Huafu Technology can meet the above electromagnetic compatibility requirements by connecting its FG terminal to the ground or to the user's case.
Protect the circuit
The switching power supply must have protection functions such as overcurrent, overheating and short circuit in the design. Therefore, the switching power supply module with complete protection functions should be preferred in the design, and the technical parameters of the protection circuit should match the working characteristics of the electrical equipment. Avoid damaging electrical equipment or switching power supplies.