What is a power adapter


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What is a power adapter

Power adapter, mainly used for small electronic equipment and electronic appliances power supply conversion equipment, generally consists of shell, power transformer and rectifier circuit. According to the connection can be divided into desktop type and wall type. According to the type of output current, it can be divided into ac output type and dc output type. At present, IT is widely supported in notebook computers, mobile phones, household IT equipment and so on.
Adapter is mainly to convert ac mains power into direct current, according to the battery specifications to provide the corresponding voltage and current, the general use of constant voltage constant current mode, it can isolate the main voltage and dangerous voltage, the fluctuation of mains power has a certain tolerance, when needed can be safely turned off. The main function of the charger is to limit the charging current to a safe level. It mainly adopts the constant current mode, which can detect the completion of charging, terminate charging according to some algorithm to extend the battery life, and terminate charging if the battery is found abnormal. These two functions can be implemented separately or combined in one physical entity.
(ii) composition and principle
The main circuit of the power adapter is composed of input electromagnetic interference filter (EMI), rectifying filter circuit, power conversion circuit, pulse width modulation (PWM) control circuit and output rectifying filter circuit. Auxiliary circuit has input over voltage protection circuit, output over voltage protection circuit, output over current protection circuit, output short circuit protection circuit and so on. Its basic composition is shown in figure 3-25. The principle of the power adapter is basically the same as that of the switching power supply. The main difference lies in that the power adapter has a single output voltage, and the switching power supply can provide multiple different output voltages to meet the power supply requirements of various loads.
With the development of electronic technology, switching power supply is becoming miniaturized and high-frequency. However, this high-frequency, the fundamental wave itself constitutes a source of interference, emitting a stronger wave of conduction interference. In addition, by improving the components to achieve high frequency, but also because of radiation interference wave will lead to a super-standard value of stray signal. These signals constitute electromagnetic interference (EMI), which is interfered with radio communications. In order to protect radio waves from electromagnetic interference, measures should be taken to limit such interference to meet relevant electromagnetic compatibility (EMC) standards or specifications. Electromagnetic interference is transmitted in two ways: conduction and radiation. Conduction transmission is a complete circuit connection between the interference source and the sensitive device, along which the interference signal is transmitted to the receiver and electromagnetic interference occurs. Radiation transmission is the interference form that the interference signal propagates outwards in the form of electromagnetic wave through the medium.

| release time：2019.09.18 Source：

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What is a power adapter