Basic knowledge of power adapter
The power adapter is known as a high-efficiency, energy-saving power supply, and it represents the development direction of stabilized power supply. At present, monolithic power adapter integrated circuits have been widely used due to their high integration, high cost performance, the simplest peripheral circuits, and the best performance indicators.
Pulse width modulation
A commonly used modulation control method in power adapters . Pulse width modulation is an analog control method, which modulates the transistor base or the gate of the MOS tube according to the change of the corresponding load to achieve the change of the on time of the transistor or the MOS tube, so as to change the output of the switching regulated power supply . Its characteristic is to keep the switching frequency constant, that is, the switching cycle 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 regulation
Cross load adjustment rate refers to the change rate of the output voltage caused by a load change in a multi-output power adapter. The change of the power supply load will cause the output of the power supply to change, the load will increase, and the output will decrease. On the contrary, the load will decrease, and the output will increase. The output change caused by a good power load change is small, usually the index is 3%-5%. It is an important indicator to measure the voltage regulator performance of the multi-output power adapter.
Work in parallel
In order to increase the output current and output power, multiple power adapters can be used in parallel. When parallel operation is required, the output voltage of each power adapter must be the same (allowing their output power to be different), and the current sharing method (referred to as the current sharing method) is used to ensure that the output current of each power adapter is based on the specified scaling factor. 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 filtering device that can effectively suppress grid noise and improve the anti-interference ability and system reliability of electronic equipment. The electromagnetic interference filter is a two-way radio frequency filter. On the one hand, it is necessary to filter external electromagnetic interference introduced from the AC grid;
On the other hand, it is also possible to avoid noise interference from its own equipment 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 input end of the power adapter.
A heat dissipation device used to reduce the operating temperature of semiconductor devices can prevent the die temperature from exceeding the maximum junction temperature due to poor heat dissipation, and enable the power adapter to perform overheating protection. The heat dissipation path is from the core to the small heat sink (or shell)> heat sink → finally to the surrounding air. There are many types of radiators, such as flat plate type, printed circuit board (PCB) type, rib type, and interdigitated type. The heat sink should be as far away from heat sources as power frequency transformers and power switching tubes.
This kind of electronic device is specially used as power output load. The electronic load can be adjusted dynamically under the control of computer. Electronic load is a device that consumes electrical energy by controlling the internal power (MOSFET) or the conduction of the transistor (the amount of the duty cycle) and relying on the power dissipated by the power tube.
The 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 referred to 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 role is to keep the AC input current in phase with the AC input voltage and filter out 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 element inductance for power factor correction. Its circuit is simple and low 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. The disadvantages are: large size and weight, difficult to obtain high power factor, working performance related to frequency, load and input voltage
Active power factor correction
Active power factor correction is referred to as APFC (also known as active PFC). Active power factor correction refers to increasing the input power factor through an active circuit (active circuit), and controlling the switching device to let the input current waveform follow the input voltage waveform. Compared to a passive power factor correction circuit (passive circuit), the inductor and capacitor are added. To be 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. The power factor can reach 0.90 ~ 0.99.
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|Release time: 2019.09.10 Source: Power adapter manufacturers|
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Dongguan Qiqi Industrial Co., Ltd. specializes in producing: power adapters , chargers, LED drive power supplies, car chargers, switching power supplies, etc ...