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Home > News > The difference and relationship between switching power supply and linear power supply

The difference and relationship between switching power supply and linear power supply

2020-05-18

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Brief introduction of Switching Power Supply:


Our common Power Supply including power adapters, chargers belong to the switching power supply. Switching power supply is a kind of power supply that maintains stable output dc voltage by controlling the ratio of switching tube opening and closing time. Generally, switching power supply is composed of pulse width modulation control IC and MOSFET field effect transistor. The high-frequency of switching power supply is the direction of its development, which miniaturizes the switching power supply and enables the switching power supply to enter a wider range of application fields, especially in the field of high and new technology, promoting the miniaturization and portability of high and new technology products. In addition, the development and application of switching power supply are of great significance in saving energy, saving resources and protecting the environment.


Principle of switching power supply:


Switching power supply mainly includes input power grid filter, input rectifier filter, inverter, output rectifier filter, control circuit, protection circuit. The following functions are introduced respectively: input power grid filter: it is used to eliminate interference ripple generated by ac power grid, such as light switch, switch of household appliances, switch of air conditioner, lightning strike, etc., and it will also prevent the high-frequency noise generated by switching power supply from diffusing to the power grid. Input rectifier filter: it is the grid input voltage for rectification filtering, to provide dc voltage for the converter; Inverter: it is a key part of the switching power supply. It transforms the dc voltage into the hf ac voltage and isolates the output from the input grid. Output rectifier filter: it rectifies and filters the high-frequency ac voltage output by the converter to obtain the required dc voltage, and at the same time prevents the interference of high-frequency noise to the load. Control circuit: test the output dc voltage and compare it with the reference voltage to enlarge it. The pulse width of the oscillator is modulated to control the converter to keep the output voltage stable. Protection circuit: when the switching power supply overvoltage, overcurrent short circuit, protection circuit to stop the switching power supply to protect the load and the power supply itself. Switching power supply is a kind of conversion device that commutates alternating current into direct current to supply power.


Advantages of switching power supply:


Small size, light weight, easy to carry, high efficiency, strong anti-interference, wide output voltage range, especially in Europe and the United States and other regions of the energy efficiency of the power supply and standby power consumption requirements after the switching power supply highlights its advantages.

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Introduction to linear power supply:


Linear power supply is to an alternating current through the transformer to reduce the voltage amplitude, again after internal rectifier rectifier circuit, direct current (dc) and pulse, after get through the filter with a small ripple of dc voltage of the power conversion device working principle of the linear power supply, linear power supply is actually in transformer output string of a power transistor, the control circuit as long as the output, a small current to the transistor's base can control the output of the triode large current, make the power system on the basis of the transformer and voltage stability at a time, so this kind of linear regulated power supply voltage regulation performance is superior to switch power or transformer 1 to 3 orders of magnitude. However, the power triode (also known as the adjustment tube) generally takes up 10 volts, and each output 1 ampere current will consume an extra 10 watts of power inside the power supply. For example, the loss of 500V 5A power supply on the power tube is 50 watts, accounting for 2% of the total output power. Therefore, the efficiency of linear power supply is slightly lower than that of the transformer.


Advantages of linear power supply: stable performance, no interference such as high frequency ripple.


Disadvantages of linear power supply: high heat and low energy efficiency. There is no extra-large power supply to choose from
The voltage feedback circuit of the linear power supply is operating in the linear (amplifying) state, while the voltage of the switching power supply is regulated by the voltage of the tube operating in the saturation and cut-off areas, that is, the switching state. Linear power supply is the output voltage sampling and then compared with the reference voltage to the voltage amplifier, the voltage amplifier output as input of the voltage adjustment pipe, used to make it across the pass transistor junction voltage changes over the input, so as to adjust the output voltage, the switching power supply is by changing the time to adjust the tube and off or change duty ratios change of output voltage.


From the point of view of its main features: linear power supply technology is mature, but I did not not low production costs, has been compared to the switching power supply in price has lost too much advantage, but can achieve a high degree of stability, linear power supply ripple is small, its interference and noise are small, but because of work in power frequency (50 hz), the volume of a transformer is larger, the efficiency is low, the overall volume is larger, appear more bulky. And the input voltage range is high; The state of high frequency switch power supply is working, the volume of a transformer is small, relatively light, but the output ripple is linear power supply, but because of its simple structure, low cost, high efficiency (the switch power supply on market efficiency can reach more than 90%) also on many occasions has replaced the linear power supply, is the trend of the development of the power supply in the future.



Best regards,

Shirley Liang

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