Comparison and difference of the advantages and disadvantages of switching power supply and linear power supply: They are all DC power supplies according to different requirements. The advantage of linear DC power supply is that it outputs linear DC power, which can be used in high-demand occasions. Switching DC power supply is the second. It consists of a transformer and a switching tube with a high switching speed. It is characterized by small weight, large capacity, and high output quality. The phase-controlled power supply is originally used in the linear power supply where the requirements are not high and the current is extremely large. The switching power supply is different from the linear power supply. Working in the amplified state, the heat is large, the efficiency is low (about 35%), a bulky heat sink is required, and a large-volume power frequency transformer is also required. The transformer will be larger when multiple sets of voltage outputs are to be produced.

The regulator tube of the switching power supply works in the saturated and cut-off state, so the heat generation is small, the efficiency is high (over 75%) and the large-volume transformer is omitted. However, the DC output of the switching power supply will be superimposed with a large ripple (50mV at 5V output typical), which can be improved by connecting a Zener diode in parallel at the output end. In addition, because the switching tube is working, a large spike interference will be generated, which also requires Connect magnetic beads in series to improve the circuit. Relatively speaking, the linear power supply does not have the above defects, and its ripple can be made very small (below 5mV).

It is better to use a switching power supply where there is a requirement for power efficiency and installation volume, and a linear power supply is more suitable for places where electromagnetic interference and power purity are required (such as capacitor leakage detection). In addition, when the circuit needs to be isolated, DC-DC is now mostly used to supply power to the isolated part (DC-DC is a switching power supply from its working principle). Also, the high frequency transformer used in the switching power supply may be troublesome to wind.

Switching power supply and linear power supply are completely different in internal structure. Switching power supply, as the name suggests, has switching action. It uses variable duty cycle or frequency conversion methods to achieve different voltages. The implementation is more complicated. The advantage is high efficiency, generally 90% Above, the disadvantage is that the wave and switching noise are large, which is suitable for occasions where the wave and noise requirements are not high; while the linear power supply has no switching action and belongs to continuous analog control. The internal structure is relatively simple, the chip area is also small, and the cost is relatively high. Low, the advantage is low cost, small wave noise, and the disadvantage is low efficiency. They have their own shortcomings and they complement each other in application!

1. The principle of linear power supply:
Linear power supplies mainly include power frequency transformers, output rectifier filters, control circuits, protection circuits, etc. The linear power supply first transforms the AC power through a transformer, and then rectifies and filters the unsteady DC voltage through a rectifier circuit. To achieve a high-precision DC voltage, the output voltage must be adjusted through voltage feedback. This power supply technology is very mature and can reach High stability, small ripple, and no interference and noise of switching power supply. But its disadvantage is that it requires a large and heavy transformer, the volume and weight of the required filter capacitor are also quite large, and the voltage feedback circuit is working in a linear state, there is a certain voltage drop on the regulator tube, and the output is relatively large. At this time, the power consumption of the adjustment tube is too large, the conversion efficiency is low, and a large heat sink must be installed. This kind of power supply is not suitable for the needs of computers and other equipment, and will gradually be replaced by switching power supplies.

2. The principle of switching power supply:
The switching power supply mainly includes input grid filter, input rectifier filter, inverter, output rectifier filter, control circuit, and protection circuit. Their functions are:

1. Input grid filter: Eliminate the interference from the grid, such as the starting of motors, switching of electrical appliances, lightning strikes, etc., and also prevent the high-frequency noise generated by the switching power supply from spreading to the grid.

2. Input rectifier filter: rectify and filter the grid input voltage to provide DC voltage to the converter.

3. Inverter: It is a key part of switching power supply. It transforms DC voltage into high frequency AC voltage, and plays a role in isolating the output part from the input power grid.

4. Output rectifier filter: rectify and filter the high frequency AC voltage output by the converter to obtain the required DC voltage, while also preventing the interference of high frequency noise to the load.

5. Control circuit: Detect the output DC voltage, compare it with the reference voltage, and amplify it. Modulate the pulse width of the oscillator to control the converter to keep the output voltage stable.

6. Protection circuit: When the switching power supply has overvoltage or overcurrent short-circuit, the protection circuit stops the switching power supply to protect the load and the power supply itself.

The switching power supply first rectifies AC power into DC power, inverts the DC power into AC power, and rectifies and outputs the required DC voltage. In this way, the switching power supply eliminates the transformer in the linear power supply and the voltage feedback circuit. The inverter circuit in the switching power supply is completely digitally adjusted, which can also achieve very high adjustment accuracy.

3. The main advantages of switching power supply:
Small size, light weight (the volume and weight are only 20-30% of the linear power supply), high efficiency (generally 60-70%, while the linear power supply is only 30-40%), its own anti-interference ability is strong, the output voltage range is wide, Modular.

The switching power supply is realized through electronic technology. The main link is: rectification into direct current-inverted into alternating current of the required voltage (mainly to adjust the voltage)-and then rectified into direct current voltage output. Since there is no transformer and heat sink in the structure of the switching power supply, the volume is very small. At the same time, there are electronic components inside the switching power supply with high efficiency and low heat generation. Although it has shortcomings such as electromagnetic interference, the current shielding technology is already in place.

Switching power supplies can be roughly divided into two types: isolated and non-isolated. The isolated type must have a switching transformer, while the non-isolated type may not necessarily have.

When the AC power supply is input, it generally needs to pass through something like a current loop to filter out the interference on the grid, and at the same time filter the interference of the power supply to the grid; when the power is the same, the higher the switching frequency, the smaller the volume of the switching transformer. But the higher the requirements for the switching tube; the secondary of the switching transformer can have multiple windings or one winding with multiple taps to obtain the required output; generally, some protection circuits should be added, such as no-load, short-circuit protection, etc. Otherwise, the switching power supply may be burnt.

Four, switching power supply & linear power supply
The main working principle of the switching power supply is that the Mos tubes of the upper bridge and the lower bridge are turned on in turn. First, the current flows in through the Mos tubes of the upper bridge. The storage function of the coil is used to accumulate electric energy in the coil. The upper bridge Mos tubes are closed and the lower bridge is opened. The MOS tube, coil and capacitor continue to supply external power. Then the lower bridge Mos tube is turned off, and the upper bridge is turned on to allow the current to enter, and this is repeated. Because the Mos tube is switched on and off in turn, it is called a switching power supply.

The linear power supply is different. Because there is no switch intervention, the water pipe is always draining water. If there is too much, it will leak out. This is the Mos tube of some linear power supplies that we often see heat up. The endless electric energy is all converted into heat energy. From this point of view, the conversion efficiency of the linear power supply is very low, and when the heat is high, the life of the component is bound to decrease, which affects the use effect.

The difference between switching power supply and linear power supply is mainly their working method:

The linear power supply power device works in a linear state, which means that the power device is always working as soon as it is used, so its work efficiency is low, generally 50% to 60%, and it must be said that it is very linear power supply. The working method of the linear power supply makes it necessary to have a voltage device to change from high voltage to low voltage. Generally, they are transformers, but there are other types like KX power supplies, which are then rectified to output DC voltage. As a result, his size is huge, heavy, low efficiency, and heat generation. He also has his advantages: small ripple, good adjustment rate, and low external interference. Suitable for use with analog circuits, various amplifiers, etc.