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Basic knowledge of power adapters

Basic knowledge of power adapters
Power adapter is known as high efficiency and energy saving power, it represents the development direction of stabilized voltage power supply. At present, monolithic power adapter integrated circuit with its high integration, high cost performance, the most simple peripheral circuit, the best performance index of the obvious advantages, has been widely used, has become the design of small power adapter preferred products.

Pulse width modulation
A modulation control commonly used in power adapters. Pulse width modulation is a kind of analog control mode, which modulates the bias of transistor base or MOS gate according to the change of corresponding load, so as to realize the change of transistor or MOS tube conduction time, so as to realize the change of output of switching stabilized power supply. Its characteristic is to keep the switch frequency constant, that is, the switch cycle is unchanged, change the pulse width, make the power adapter output voltage change minimum when the power grid voltage and load change
Cross - load adjustment
Cross-load regulation refers to the rate of change of output voltage of each circuit when the load of one circuit in a multi-circuit output power adapter changes. The change of power load will cause the change of power output, the load increases, the output decreases, conversely, the load decreases, the output increases. Good power load changes result in smaller output changes, usually in the range of 3% to 5%. It is an important index to measure the stable voltage performance of multichannel output power adapter.
Parallel operation
To improve the output current and power, multiple power adapters can be used in parallel. Parallel operation requires that the output voltage of each power adapter must be the same (allowing them to have different output power), and the equipartition current method (called mean current method) is used to ensure that the output current of each power adapter is distributed according to the specified proportional coefficient.
Electromagnetic interference filter
EMI 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. Electromagnetic interference filter is a kind of filter device which can effectively suppress the noise of power grid and improve the anti-interference ability and system reliability of electronic equipment.
On the other hand, it can 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 emi filter can suppress both serial mode interference and common mode interference. The emi filter shall be connected to the ac input end of the power adapter.
The radiator
A heat dissipation device used to reduce the operating temperature of semiconductor devices, which can avoid the core temperature exceeding the maximum junction temperature due to poor heat dissipation and make the power adapter overheat protection. Cooling way from 亠 small tube core cooling plate (or package) > the radiator and finally into the surrounding air. Radiator plate, printed board (PCB) type, rib type, fork finger type and other types. Radiator should be as far as possible away from power frequency transformer, power switch tube and other heat sources.
Electronic load
It is an electronic device specially designed for 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 transistor's conduction flux (duty cycle), depending on the dissipated power of the power tube.
The power factor
The size of the Power Factor is related to the nature of the load on the circuit. It represents the ratio of active power to apparent power.
Power factor correction
PFC for power factor correction. Power factor correction technique is defined as: power factor (PF) is the ratio of active power P to apparent power s. Its function is to keep the ac input current in phase with the ac input voltage and filter the current harmonics, so as to raise the power factor of the equipment to a predetermined value close to 1
Passive power factor correction
Passive power factor correction is referred to as PPFC. It USES passive inductance to carry on the power factor correction, its circuit is simple, the cost is low, but easy to produce noise and can only raise 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, and performance is related to frequency, load and input voltage
Active power factor correction
Active power factor correction (APFC) for short. Active power factor correction is to point to by active circuit (active circuit) to improve the input power factor, control switch device to input current waveform to follow the input voltage waveform, compared with the passive power factor correction circuit (passive circuit) are more complex by adding the inductance and capacitance, the improvement of power factor better, but costs are higher, reliability will be reduced. It is to add a power conversion circuit between the input rectifier bridge and the output filter capacitor to correct the input current into sinusoidal wave with the same phase as the input voltage, and the power factor can reach 0.90~0.99.
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