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Linear, switching power supply

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Linear, switching power supply
Issue Time:2020-04-28
TITLE:What is the difference between a switching power supply and a linear power supply?

Linear power supply and switching power supply have their unique features in different scenarios. For example, linear power supply can be used in very demanding situations, because the output of linear power supply is direct current. If it is a large current is suitable for the use of switching power supply, because the switching power supply has the advantages of small weight, large capacity, high output quality.

The adjustment tube of linear power supply works in the state of amplification, so the heat is large, the efficiency is low (35% or so), the need to add a large volume of the radiator, but also need to be a large volume of the power frequency transformer, when the transformer will be more large to produce multiple sets of voltage output.

The adjustment tube of switching power supply works in the saturation and cutoff state, thus producing less heat, high efficiency (75% above) and eliminating the large volume of the transformer. However, the dc output of the switching power supply will be superimposed on a large ripple (50mV at 5V output typical), in the output end and connected to a stabilized diode can be improved, in addition, because the switching tube work will produce a large spike pulse interference, also need to be in the circuit series magnetic beads to improve. Relative to linear power supply without the above defects, its ripple can be done very small (below 5mV).

It is better to use switching power supply where there are requirements for power supply efficiency and installation volume, and more linear power supply where there are requirements for electromagnetic interference and power purity (such as capacitor leakage detection). In addition, when isolation is needed in the circuit, dc-dc is now used to supply power to the isolated part (dc-dc is the switching power supply from its working principle). Also, the high frequency transformer used in the switching power supply may be more difficult to wind

Switching power supply and linear power supply on the internal structure is not the same, just as its name implies is to switch power supply switch action, it USES variable duty cycle or realizes different version for different voltage, frequency conversion to realize more complex, the biggest advantage is high efficiency, generally over 90%, the disadvantage is that Wen Bo and switching noise is bigger, suitable for Wen Bo and requiring low noise; The linear power supply has no switch action, which belongs to continuous analog control. The internal structure is relatively simple, the chip area is small, the cost is low, the advantages are low cost, small noise, the biggest disadvantage is low efficiency. They each have shortcomings in the application of complementary coexistence!

The linear power source power device works in the linear state, that is to say, he used the power device is always working, so it leads to his work efficiency is low, generally in 50%~60%, also have to say that he is a very good linear power source. The working mode of linear power supply makes it necessary to have a voltage transfer device from high voltage to low voltage, which is generally a transformer, and there are other sources like KX power supply, and then output dc voltage through rectification. This makes it bulky, cumbersome, inefficient and calorific. He also has his advantages: small ripple, good adjustment rate, little external interference. Suitable for analog circuits, amplifiers, etc

Switching power supply. His power devices working in switch state, (a open, one open a level, frequency very fast, generally flat frequency switch power supply in 100 ~ 200 KHZ, module power supply in 300 ~ 500 KHZ). So that his loss is small, efficiency is high, the transformer has a request, the high permeability of the material to do. A little ink, transformer which is small a word. The efficiency of 80% ~ 90%. It is said that the best American VICOR modules is as high as 99%. The efficiency of switch power supply high volume is small, but and linear power supply ripple than he, and voltage current regulation have discount.

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