Basic knowledge of power adapter

　　A modulation control method commonly used in power adapters. Pulse width modulation is an analog control method that modulates the bias of the transistor base or the MOS transistor gate according to the change of the corresponding load to realize the change of the transistor or MOS transistor conduction time, thereby realizing the change of the output of the switching stabilized power supply . Its characteristic is to keep the switching frequency constant, that is, the switching period is unchanged, and the pulse width is changed to minimize the change in the output voltage of the power adapter when the grid voltage and load change.

　　Cross load adjustment rate

　　The cross-load adjustment rate refers to the rate of change of the output voltage of each channel caused by a change in the load of one of the multiple output power adapters. The change of the power load will cause the change of the output of the power supply. The load increases and the output decreases. On the contrary, the load decreases and the output increases. The output change caused by the load change of a good power supply is small, usually the index is 3%-5%. It is an important indicator to measure the voltage regulation performance of a multi-output power adapter.

　　Parallel operation

　　To increase the output current and output power, multiple power adapters can be used in parallel. When running in parallel, the output voltage of each power adapter must be the same (their output power is allowed to be different), and the current sharing method (referred to as the current sharing method) is adopted to ensure that the output current of each power adapter is in accordance with the specified proportional coefficient. distribution.

　　Electromagnetic interference filter

　　Electromagnetic interference filter, also known as "EMI filter" is an electronic circuit device used to suppress electromagnetic interference, especially noise in power lines or control signal lines. A filter device that can effectively suppress grid noise and improve the anti-interference ability of electronic equipment and system reliability. Electromagnetic interference filters are two-way radio frequency filters. On the one hand, they must filter out external electromagnetic interference introduced from the AC power grid;

　　On the other hand, it can also prevent its own equipment from emitting noise interference to the outside, so as not to affect the normal operation of other electronic equipment in the same electromagnetic environment. The electromagnetic interference filter can suppress both series mode interference and common mode interference. The electromagnetic interference filter should be connected to the AC inlet end of the power adapter.

　　heat sink

　　A heat dissipation device used to reduce the operating temperature of semiconductor devices, which can prevent the die temperature from exceeding the maximum junction temperature due to poor heat dissipation, and the power adapter is protected from overheating. The way of heat dissipation is from the small heat sink (or shell) of the die, the heat sink, and finally to the surrounding air. There are many types of radiators such as flat plate type, printed circuit board (PCB) type, rib type and interdigital type. The radiator should be as far away as possible from heat sources such as power frequency transformers and power switch tubes.

　　Electronic load

　　An electronic device specially used as a power output load. The electronic load can be dynamically adjusted under the control of a computer. The electronic load is a device that consumes electric energy by controlling the internal power (MOSFET) or the conductance of the transistor (the amount of duty cycle) and the power dissipation of the power tube.

　　Power factor

　　The power factor (Power Factor) is related to the load nature of the circuit. It represents the ratio of active power to apparent power.

　　Power factor correction

　　Power factor correction is abbreviated as PFC. The definition of power factor correction technology is: power factor (PF) is the ratio of active power P to apparent power s. Its function is to keep the AC input current and the AC input voltage in the same phase and filter out the current harmonics, and increase the power factor of the device to a predetermined value close to 1.

　　Passive power factor correction

　　Passive power factor correction is referred to as PPFC (also known as passive PFC). It uses passive component inductance for power factor correction. Its circuit is simple and low in cost, but it is prone to noise and can only increase the power factor to about 80%. The main advantages of passive power factor correction are: simple, low cost, reliable, and small emi, but the disadvantages are: large size and weight, it is difficult to obtain high power factor, working performance is related to frequency, load and input voltage

　　Active power factor correction

　　Active power factor correction is abbreviated as APFC (also known as active PFC). Active power factor correction means that the input power factor is improved through the active circuit (active circuit), and the switching device is controlled to make the input current waveform follow the input voltage waveform. Compared with the passive power factor correction circuit (passive circuit) by adding inductance and capacitance It is more complicated, the improvement of the power factor is better, but the cost is higher, and the reliability will be reduced. It adds a power conversion circuit between the input rectifier bridge and the output filter capacitor to correct the input current into a sine wave with the same phase as the input voltage without distortion, and the power factor can reach 0.90~0.99.

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