Offline switching power supply, also called isolated switching power supply, is an AC-DC conversion circuit. AC and DC are isolated by a transformer.
In some laboratories or high-demand occasions, for the safety of the experimenters, the input power of the experiment is generally isolated from the mains with a 1:1 industrial frequency transformer, so that no matter which line of the line is touched by the laboratory experimenter There is no danger of electric shock to the root wire because the isolated power supply is not connected to the earth.
In industrial control equipment, power ground isolation between two systems is sometimes required, such as isolation of ground noise, isolation of high common-mode voltage, etc., a DC converter with a transformer is used to separate the two power supplies to make They are independent of each other, so as to achieve the above purpose! Each module is powered separately to prevent one module from being damaged by high voltage discharge or other reasons and causing damage to other modules. The purpose of this is to ensure that each module works independently without interference.
The traditional transistor series regulated power supply is a continuously controlled linear regulated power supply. This traditional regulated power supply technology is relatively mature. And there are a large number of integrated linear stabilized power supply modules, which have the characteristics of good stable performance, low output ripple voltage, and reliable use.
However, it usually requires a large and heavy industrial frequency transformer and isolation, and the size and weight of the filter are also very large. The regulator tube works in a linear amplification state. In order to ensure the stable output voltage, the collector and emitter must withstand a large voltage difference, which leads to the large power consumption of the regulator tube and low power supply efficiency, generally only about 45%. In addition, because the adjustment tube consumes a lot of power, it is necessary to use a high-power adjustment tube and be equipped with a large radiator, so it is difficult to meet the requirements of the development of electronic equipment.
This has led to the rapid development of switching power supplies with high efficiency, small size, and lightweight. Switching regulated power supplies use power semiconductor devices like switches, and adjust the output voltage by controlling the duty cycle of the switches. Take the power transistor (GTR) as an example. When the switching tube is saturated and turned on, the voltage drop across the collector and emitter is close to zero(SCIENTEK ELECTRICAL). When the switching tube is turned off, its collector current is zero, so its power consumption is small and the efficiency is high. Up to 70%~95%. The power consumption is small, and the radiator is also reduced. At the same time, the switch-mode regulated power supply directly rectifies and filters the grid voltage, and then the switch adjusts the regulator to stabilize it, without the need for a power transformer; in addition, the switching frequency is in the dozens of kHz, filter capacitor, inductor value is small.
Therefore, the switching power supply has the characteristics of lightweight and small size. In addition, due to low power consumption and low internal temperature rise, the stability and reliability of the whole machine are improved. Moreover, its adaptability to the power grid has also been greatly improved. Generally, series regulated power supplies allow grid fluctuation range of 220V+10%, while switch-type regulated power supplies can be stable when the grid voltage changes from 110V to 260V. The output voltage.
Off-line switching power supply design and the increasing popularity of electronic products have brought new opportunities and challenges to power management chips. Switching power supplies are widely used in various electronic products due to their small size and high efficiency.