The difference between a switching DC power supply and a linear DC power supply

Comparison and difference between the advantages and disadvantages of switching power supply and linear power supply: they are DC power supplies used differently according to requirements, the advantage of linear DC power supply is that he outputs linear DC power, which can be used in occasions with high requirements, and the switching DC power supply is secondary, he is made of transformers and switch tubes with very high switching speed, characterized by small weight, large capacity, high output quality, phased electric original used in the case of low requirements, large current linear power supply, switching power supply difference linear power supply adjustment tube works in an amplified state, so the heat is large, The efficiency is low (about 35%), and a large heat sink is required, and a power frequency transformer that is also large is also required, and the transformer will be larger when multiple sets of voltage outputs are to be made.

The adjustment tube of the switching power supply works in the saturation and cut-off state, so the heat generation is small, the efficiency is high (more than 75%), and the large volume of the transformer is omitted. However, the DC output of the switching power supply will be superimposed on a large ripple (50mV at 5V output typical), and the voltage regulator diode can be connected at the output end, and because the switch tube work will produce a large spike pulse interference, it is also necessary to connect magnetic beads in the circuit to improve. Relatively speaking, the linear power supply does not have the above defects, and its ripple can be very small (less than 5mV).

It is better to use a switching power supply for places where power supply efficiency and installation volume are required, and linear power supplies are preferred for places where electromagnetic interference and power supply purity are required (such as capacitance leakage detection). In addition, when the circuit needs to be isolated, most of the current DC-DC is used to supply the isolated part of the power supply (DC-DC is a switching power supply in terms of its working principle). In addition, the high-frequency transformers used in switching power supplies may be troublesome to wind.

Switching power supply and linear power supply are completely different in the internal structure, switching power supply as the name suggests has switching action, it uses the method of variable duty cycle or frequency conversion to achieve different voltages, the realization is more complex, the advantage is high efficiency, generally more than 90%, the disadvantage is that the text wave and switching noise is larger, suitable for the occasion that the text wave and noise requirements are not high; The linear power supply has no switching action, belongs to continuous analog control, the internal structure is relatively simple, the chip area is also small, the cost is low, the advantage is low cost, the text wave noise is small, and the disadvantage is low efficiency. They all have their own disadvantages and complement each other in terms of application!

First, the principle of linear power supply:

       Linear power supply mainly includes power frequency transformer, output rectifier filter, control circuit, protection circuit, etc. Linear power supply is the first alternating current through the transformer transformer, and then through the rectifier circuit rectification filter to obtain the unstable DC voltage, to achieve high-precision DC voltage, must be adjusted through voltage feedback output voltage, this power supply technology is very mature, can achieve a high degree of stability, ripple is also very small, and there is no interference and noise of switching power supply. But its disadvantage is that it needs a large and bulky transformer, and the volume and weight of the required filter capacitor are also quite large, and the voltage feedback circuit is working in a linear state, and there is a certain voltage drop on the adjustment tube, and when the output is larger than the working current, the power consumption of the adjustment tube is too large, the conversion efficiency is low, and a large heat sink is installed. This power supply is not suitable for the needs of computers and other equipment, and will be gradually replaced by switching power supplies.

Second, 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 power grid filter: eliminate the interference from the power grid, such as the start of the motor, the switch of electrical appliances, lightning strikes, etc., and also prevent the high-frequency noise generated by the switching power supply from spreading to the power grid.

2. Input rectifier filter: the input voltage of the power grid is rectified and filtered to provide DC voltage for the converter.

3. Inverter: It is a key part of the switching power supply. It converts the DC voltage into a high-frequency AC voltage and isolates the output from the input grid.

4. Output rectifier filter: the high-frequency AC voltage output by the converter is rectified and filtered to obtain the required DC voltage, and at the same time, it also prevents 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. Modulates the pulse width of the oscillator to control the converter to keep the output voltage stable.

6. Protection circuit: When the switching power supply is over-voltage and over-current short circuit, the protection circuit makes the switching power supply stop working to protect the load and the power supply itself.

The switching power supply is to rectify the alternating current into direct current first, then reverse the DC into alternating current, and output it into the required DC voltage after rectification. In this way, the switching power supply eliminates the need for a transformer in the linear power supply, as well as a voltage feedback circuit. The inverter circuit in the switching power supply is completely digitally adjusted, which can also achieve very high adjustment accuracy.

Third, the main advantages of switching power supply:

      Small size, light weight (volume and weight are only 20~30% of linear power supply), high efficiency (generally 60~70%, while linear power supply is only 30~40%), strong self-anti-interference, wide output voltage range, modularization.

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

Switching power supply can be roughly divided into isolated and non-isolated, isolated type must have switching transformer, non-isolated may not necessarily have.

When the AC power is input, it generally has to pass through something like the ehrosphere to filter out the interference on the power grid, and also filter out the interference of the power supply to the power 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 stage of the switching transformer can have multiple windings or one winding with multiple taps to get the required output; Generally, some protection circuits should be added, such as no-load, short circuit and other protection, otherwise the switching power supply may be burned.

4. Switching power supply & linear power supply

      The main working principle of switching power supply is that the Mos tube of the upper and lower bridge is turned on in turn, first the current flows through the upper wall Mos tube, and the electric energy is concentrated in the coil by using the storage function of the coil, and the upper wall Mos tube is closed, and the Mos tube of the lower bridge is opened, and the coil and capacitor continue to supply power to the outside. Then close the lower side Mos tube, and then open the upper side to let the current enter, and repeat it like this, because it is necessary to turn on and off the Mos tube, so it is called switching power supply.

The linear power supply is different, because there is no switch intervention, so that the water pipe has been discharging water, if there is more, it will leak out, this is what we often see that the Mos tube of some linear power supply generates a lot of heat, and the inexhaustible electrical energy is all converted into thermal 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, affecting the use effect.

The difference between switching power supplies and linear power supplies is mainly how they work:

The linear power supply power device works in a linear state, that is to say, the power device has been working as soon as he uses it, so it also leads to his low work efficiency, generally in 50% ~ 60%, and it has to be said that he is a good linear power supply. The working mode of the linear power supply makes it necessary to have a voltage device from high voltage to low voltage, generally transformer, there are others like KX power supply, and then output DC voltage through rectification. As a result, he is bulky, bulky, inefficient, and generates a lot of heat. He also has his advantages: small ripple, good adjustment rate, and little external interference. It is suitable for analog circuits, various amplifiers, etc.

Comparison and difference between the advantages and disadvantages of switching power supply and linear power supply: they are DC power supplies used differently according to requirements, the advantage of linear DC power supply is that he outputs linear DC power, which can be used in occasions with high requirements, and the switching DC power supply is secondary, he is made of transformers and switch tubes with very high switching speed, characterized by small weight, large capacity, high output quality, phased electric original used in the case of low requirements, large current linear power supply, switching power supply difference linear power supply adjustment tube works in an amplified state, so the heat is large, The efficiency is low (about 35%), and a large heat sink is required, and a power frequency transformer that is also large is also required, and the transformer will be larger when multiple sets of voltage outputs are to be made.

The adjustment tube of the switching power supply works in the saturation and cut-off state, so the heat generation is small, the efficiency is high (more than 75%), and the large volume of the transformer is omitted. However, the DC output of the switching power supply will be superimposed on a large ripple (50mV at 5V output typical), and the voltage regulator diode can be connected at the output end, and because the switch tube work will produce a large spike pulse interference, it is also necessary to connect magnetic beads in the circuit to improve. Relatively speaking, the linear power supply does not have the above defects, and its ripple can be very small (less than 5mV).

It is better to use a switching power supply for places where power supply efficiency and installation volume are required, and linear power supplies are preferred for places where electromagnetic interference and power supply purity are required (such as capacitance leakage detection). In addition, when the circuit needs to be isolated, most of the current DC-DC is used to supply the isolated part of the power supply (DC-DC is a switching power supply in terms of its working principle). In addition, the high-frequency transformers used in switching power supplies may be troublesome to wind.

Switching power supply and linear power supply are completely different in the internal structure, switching power supply as the name suggests has switching action, it uses the method of variable duty cycle or frequency conversion to achieve different voltages, the realization is more complex, the advantage is high efficiency, generally more than 90%, the disadvantage is that the text wave and switching noise is larger, suitable for the occasion that the text wave and noise requirements are not high; The linear power supply has no switching action, belongs to continuous analog control, the internal structure is relatively simple, the chip area is also small, the cost is low, the advantage is low cost, the text wave noise is small, and the disadvantage is low efficiency. They all have their own disadvantages and complement each other in terms of application!

First, the principle of linear power supply:

       Linear power supply mainly includes power frequency transformer, output rectifier filter, control circuit, protection circuit, etc. Linear power supply is the first alternating current through the transformer transformer, and then through the rectifier circuit rectification filter to obtain the unstable DC voltage, to achieve high-precision DC voltage, must be adjusted through voltage feedback output voltage, this power supply technology is very mature, can achieve a high degree of stability, ripple is also very small, and there is no interference and noise of switching power supply. But its disadvantage is that it needs a large and bulky transformer, and the volume and weight of the required filter capacitor are also quite large, and the voltage feedback circuit is working in a linear state, and there is a certain voltage drop on the adjustment tube, and when the output is larger than the working current, the power consumption of the adjustment tube is too large, the conversion efficiency is low, and a large heat sink is installed. This power supply is not suitable for the needs of computers and other equipment, and will be gradually replaced by switching power supplies.

Second, 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 power grid filter: eliminate the interference from the power grid, such as the start of the motor, the switch of electrical appliances, lightning strikes, etc., and also prevent the high-frequency noise generated by the switching power supply from spreading to the power grid.

2. Input rectifier filter: the input voltage of the power grid is rectified and filtered to provide DC voltage for the converter.

3. Inverter: It is a key part of the switching power supply. It converts the DC voltage into a high-frequency AC voltage and isolates the output from the input grid.

4. Output rectifier filter: the high-frequency AC voltage output by the converter is rectified and filtered to obtain the required DC voltage, and at the same time, it also prevents 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. Modulates the pulse width of the oscillator to control the converter to keep the output voltage stable.

6. Protection circuit: When the switching power supply is over-voltage and over-current short circuit, the protection circuit makes the switching power supply stop working to protect the load and the power supply itself.

The switching power supply is to rectify the alternating current into direct current first, then reverse the DC into alternating current, and output it into the required DC voltage after rectification. In this way, the switching power supply eliminates the need for a transformer in the linear power supply, as well as a voltage feedback circuit. The inverter circuit in the switching power supply is completely digitally adjusted, which can also achieve very high adjustment accuracy.

Third, the main advantages of switching power supply:

      Small size, light weight (volume and weight are only 20~30% of linear power supply), high efficiency (generally 60~70%, while linear power supply is only 30~40%), strong self-anti-interference, wide output voltage range, modularization.

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

Switching power supply can be roughly divided into isolated and non-isolated, isolated type must have switching transformer, non-isolated may not necessarily have.

When the AC power is input, it generally has to pass through something like the ehrosphere to filter out the interference on the power grid, and also filter out the interference of the power supply to the power 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 stage of the switching transformer can have multiple windings or one winding with multiple taps to get the required output; Generally, some protection circuits should be added, such as no-load, short circuit and other protection, otherwise the switching power supply may be burned.

4. Switching power supply & linear power supply

      The main working principle of switching power supply is that the Mos tube of the upper and lower bridge is turned on in turn, first the current flows through the upper wall Mos tube, and the electric energy is concentrated in the coil by using the storage function of the coil, and the upper wall Mos tube is closed, and the Mos tube of the lower bridge is opened, and the coil and capacitor continue to supply power to the outside. Then close the lower side Mos tube, and then open the upper side to let the current enter, and repeat it like this, because it is necessary to turn on and off the Mos tube, so it is called switching power supply.

The linear power supply is different, because there is no switch intervention, so that the water pipe has been discharging water, if there is more, it will leak out, this is what we often see that the Mos tube of some linear power supply generates a lot of heat, and the inexhaustible electrical energy is all converted into thermal 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, affecting the use effect.

The difference between switching power supplies and linear power supplies is mainly how they work:

The linear power supply power device works in a linear state, that is to say, the power device has been working as soon as he uses it, so it also leads to his low work efficiency, generally in 50% ~ 60%, and it has to be said that he is a good linear power supply. The working mode of the linear power supply makes it necessary to have a voltage device from high voltage to low voltage, generally transformer, there are others like KX power supply, and then output DC voltage through rectification. As a result, he is bulky, bulky, inefficient, and generates a lot of heat. He also has his advantages: small ripple, good adjustment rate, and little external interference. It is suitable for analog circuits, various amplifiers, etc.