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The structure and characteristics of linear power adapter

source:Industry News     Popular:adapter     release time:2020-12-16 18:16:56     Article author:sznbone    

The switching power supply is different from the linear power adapter. The former regulator tube works in the on and off state, and the latter regulator tube works in the linear state. The power adapter realizes voltage stabilization by controlling the on and off time of the regulator tube. The advantages of the power adapter are small size, light weight, low power consumption, wide voltage regulation range, and efficiency up to 80% to 90%. The power loss of the regulator tube is small, and the radiator is also reduced accordingly. The operating frequency of the British standard power adapter is tens of kilohertz or even hundreds of kilohertz. The filter inductance and capacitance components can be used with a smaller capacity, and the allowable ambient temperature can also be greatly increased. It is widely used in various electronic devices. This chapter mainly introduces the basic composition, classification and working principle of the power adapter, so that readers have a preliminary understanding of the power adapter.

Comparison of regulated power adapter

Electronic equipment cannot do without power adapter. The power adapter supplies the energy required by the electronic equipment. The performance and quality of power adapters directly affect the safe and reliable operation of electronic devices, so the requirements for the performance and quality of power adapters for electronic devices are getting higher and higher. There are two main types of existing power adapters: series linear regulated power adapters (referred to as linear power adapters) and switching regulated power adapters (referred to as power adapters). These two types of power adapters have their own characteristics and are widely used.

 

The structure and characteristics of linear power adapter

The block diagram and output waveform of the linear power adapter are shown in the figure.

 

Figure Linear power adapter block diagram and output waveform

Linear power adapters are usually obtained from AC power provided by the power grid through transformation, rectification, filtering and stabilization. The functions of each part of the circuit are as follows:

①The power adapter transformer-converts the 220V grid voltage into the AC voltage required by the rectifier circuit, and a small number of circuits use capacitors to step down, such as remote-control electric fan circuits.

② Rectifier circuit-convert AC voltage into pulsating DC voltage. Commonly used rectifier circuits include half-wave rectifier circuits, full-wave rectifier circuits and bridge rectifier circuits.

③Filter circuit-converts the pulsating DC voltage into a smoother DC voltage. The filter circuits commonly used in linear power adapters include inductance filter, capacitor filter and resistance-capacitance filter. The most commonly used one is capacitor filter.

④Stabilizing circuit-stabilize the output voltage of the DC power adapter, basically not affected by the grid voltage or load. The voltage stabilizing circuits commonly used in linear power adapters include diode stabilization and series stabilization. Among them, there are ready-made integrated circuits for series voltage stabilization, such as fixed voltage output integrated circuits such as LM78××, LM79××, etc., and adjustable voltage output integrated circuits such as LM317 and LM337.

The picture shows a linear stabilized power supply adapter with 4 functional modules including mains voltage step-down, rectification, filtering and voltage stabilization.

 

 

 

Linear regulated power adapter with 4 functional modules

 

The advantages of the linear power adapter are good stability, fast transient response, high reliability, high output voltage accuracy and low output ripple voltage; the disadvantage is the low operating frequency, the volume and weight of the power frequency transformer and filter used Both are larger. The adjustment tube works in a linear state, has high power consumption and low efficiency, and requires an additional radiator. In general, the efficiency of the linear power adapter will not exceed 50%, but its excellent output characteristics,


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