Knowledge about switch mode power supply

Switch Mode Power Supply (SMPS), also known as switching power supply and switching converter, is a high-frequency power conversion device and a type of power supply. Its function is to convert a level of voltage into the voltage or current required by the user through different forms of architecture. The input of a switching power supply is mostly AC power (such as mains) or DC power, and the output is mostly equipment that requires DC power, such as a personal computer, and the switch mode power supply converts the voltage and current between the two.

Switch mode power supplies are different from linear power supplies. Most of the switching transistors used by switch mode power supplies switch between fully open mode (saturation area) and fully closed mode (cutoff area). Both modes have the characteristics of low dissipation. The conversion will have higher dissipation, but the time is very short, so it saves energy and generates less waste heat. Ideally, the switching power supply itself consumes no power. Voltage regulation is achieved by adjusting the turn-on and turn-off times of transistors. On the contrary, when a linear power supply generates an output voltage, the transistor works in the amplification area and consumes power itself. The high conversion efficiency of the switch mode power supply is one of its major advantages, and because the switch mode power supply has a high operating frequency, it can use a small-sized, lightweight transformer. Therefore, the switch mode power supply will be smaller and lighter than a linear power supply.

If high efficiency, size and weight of the power supply are important considerations, switch mode power supplies are better than linear power supplies. However, the switch mode power supply is more complicated, and the internal transistors will switch frequently. If the switching current is not processed, noise and electromagnetic interference may be generated that affects other equipment. Moreover, if the switch mode power supply is not specially designed, its power factor may not be high.

There are two types of modern switch mode power supplies: one is DC switch mode power supply; the other is AC switch mode power supply. What is mainly introduced here is only the DC switch mode power supply. Its function is to convert the original power supply (coarse power) with poor power quality, such as mains power or battery power, into a higher quality DC voltage (fine power) that meets the requirements of the equipment. . The core of the DC switch mode power supply is the DC/DC converter. Therefore, the classification of DC switch mode power supplies relies on the classification of DC/DC converters. In other words, the classification of DC switch mode power supplies is basically the same as the classification of DC/DC converters. The classification of DC/DC converters is basically the classification of DC switch mode power supplies.

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