What is the difference between switching power supply and linear power supply?

Comparison and difference between the advantages and disadvantages of switching power supply and linear power supply, are DC power supply according to different requirements use of different differences, linear DC power supply is the best. It output is linear direct current, which can be used in high demand occasions, switching DC power supply followed by,it is a high switching speed of the transformer and switching tube, characterized by small weight, large capacity, high output quality, phase-controlled electrical source used in low demand, the occasion of large current linear power supply, the difference between linear power supply adjustment tube work in the state of amplification, so the heat is large, Low efficiency (35% or so), you need to add a large volume of heat sink, but also need is also a large volume of power frequency transformer, when to make multiple groups of voltage output transformer will be larger.

The adjusting tube of the switching power supply works in the saturated and up state, so the heat is small, the efficiency is high (more than 75%) and the large volume transformer is eliminated. However, the DC output will be superimposed on the larger ripple, and the voltage regulator diode at the output end can be improved, in addition, because the switching tube work will produce a large spike pulse interference, it also needs to be connected in the circuit to improve the magnetic beads. In contrast, linear power supplies do not have the above defects, and their ripple can be made very small (under 5mV).

Switching power supply is preferred where power efficiency and installation volume are required, and linear power supply is preferred where electromagnetic interference and power purity are required (such as capacitor leakage detection). In addition, when the circuit needs to be isolated, most now use DC-DC to do the isolated part of the power supply (DC-DC from its working principle is switching power supply). In addition, the high-frequency transformer used in the switching power supply may be more trouble to wind up the switching power supply and linear power supply in the internal structure is completely different, as the name implies switching action, it uses the change duty ratio or frequency conversion method to achieve different voltages, the realization is more complex, the biggest advantage is high efficiency, generally more than 90%, the disadvantage is that the wave and switching noise is larger, It is suitable for the occasions where the requirement of text wave and noise is not high. The linear power supply has no switching action, which belongs to continuous analog control. The internal structure is relatively simple, the chip area is small, and the cost is low. The advantages are low cost, small noise of the wave, and the biggest disadvantage is low efficiency. They each have shortcomings in the application of complementary coexistence!

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 alternating current through the transformer transformer, and then through the rectifier circuit rectifier filtering to get unstable DC voltage, to achieve high precision DC voltage, must be adjusted by voltage feedback output voltage, this power technology is very mature, can achieve high stability, ripple is very small, and there is no switching power supply with interference and noise. But its disadvantage is that it needs a large and bulky transformer, the volume and weight of the filter capacitor is also quite large, and the voltage feedback circuit is working in a linear state, the adjustment tube has a certain voltage drop, in the output of a large working current, resulting in the adjustment tube power consumption is too large, conversion efficiency is low, but also install a large heat sink. This kind of power supply is not suitable for computer and other equipment needs, will be gradually replaced by switching power supply.

Two, principle:

It mainly includes input power grid filter, input rectifier filter, inverter, output rectifier filter, control circuit, 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., but also prevent the high-frequency noise generated by the switching power supply from spreading to the power grid.

2, input rectifier filter: the power grid input voltage for rectifier filtering, to provide DC voltage for the converter.

3, inverter: is a key part of the switching power supply. It converts DC voltage into high-frequency AC voltage and acts as a barrier between the output and the input grid.

4, output rectifier filter: the converter output high-frequency AC voltage rectifier filter to get the required DC voltage, but also to prevent high-frequency noise interference to the load.

5, control circuit: detect the output DC voltage, and compare it with the reference voltage, for amplification. Modulates the pulse width of the oscillator, thereby controlling the converter to keep the output voltage stable.

6, protection circuit: when the switching power supply occurs over voltage, over current short circuit, the protection circuit makes the switching power supply stop working to protect the load and power itself.

Switching power supply is the alternating current first commutated into direct current, in the DC inverter into alternating current, in the rectifier output into the required DC voltage. This eliminates the need for a transformer and a voltage feedback circuit in a linear power supply. The inverter circuit of switching power supply is completely digital adjustment, also can achieve very high adjustment precision.

Main advantages:

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

Main disadvantages:

Due to the high-frequency voltage generated in the inverter circuit, there is a certain interference to the surrounding equipment. The need for good shielding and grounding switching power supply is to use the circuit control switch tube for high-speed channel pass and cut-off. The direct current into a high frequency of alternating current to provide transformer transformer voltage, so as to produce the required one or more groups of voltage! The reason for switching to Huawei HF AC is that the efficiency of HF AC in transformer transformer circuit is much higher than that of 50Hz. So the switching transformer can be made very small, and the work is not very hot!! The cost is very low. There is no point in switching power if you don't change 50Hz to high frequency!! Switching transformers are no mystery. It's just an ordinary transformer! This is the switching power supply.

Switching power supply, is realized through electronic technology, the main link: rectifier into DC - inverter into the required voltage of alternating current (mainly to adjust the voltage) - and then through the rectifier into DC voltage output.

The structure of switching power supply is very small because there is no transformer and heat sink in the middle. At the same time, the interior are electronic components, high efficiency, low heat. Although, with electromagnetic interference and other shortcomings, but now the shielding technology has been very in place.

Switching power supply can be divided into isolation and non-isolation of two types, isolation must have switching transformers, but not necessarily isolated.

The working principle is:

1. The AC power input is rectified and filtered into DC;

2. Through high frequency PWM(pulse width modulation) signal control switch tube, add the DC to the switch transformer primary;

3. Switching transformer secondary induction of high frequency voltage, through the rectification filter to supply the load;

4. The output part is fed back to the control circuit through a certain circuit to control the PWM duty ratio, so as to achieve the purpose of stable output.

When AC power is input, it usually goes through something like the current coil to filter out the interference on the grid, and also filter out the interference of the power supply on the grid. At the same power, the higher the switching frequency, the smaller the volume of the switching transformer, but the higher the requirements of the switching tube; The secondary of the switching transformer can have multiple windings or one winding has multiple taps to obtain the desired output; Generally, some protection circuits should be added, such as no-load, short circuit and other protection, otherwise it may burn the switching power supply.

So that's basically how it works.

In fact, there are now very high integration of the dedicated chip, can make the peripheral circuit is very simple, even do not debug.

TOP series chips (or modules), for example, can be made into a basic switching power supply by combining some resistance-tolerance components and a switching transformer.

Switching power supply & linear power supply

The main working principle is that the Mos tube of the upper bridge and the lower bridge is switched on in turn. First, the current flows through the Mos tube of the upper bridge, and the storage function of the coil is used to gather the electric energy in the coil. Finally, the Mos tube of the upper bridge is closed, and the Mos tube of the lower bridge is opened. And then close the lower bridge Mos tube, and then open the upper bridge to let the current into, so repeated, because to switch Mos tube in turn, so called switching power supply.

And linear power is not the same, because there is no switch involved, so that the water pipe has been releasing water, if there is much, it will leak out, which is what we often see in some linear power Mos tube heat is very large, the use of electricity, all converted into heat. From this point of view, the conversion efficiency of linear power supply is very low, and when the heat is high, the life of the component is bound to decline, affecting the final use effect.

      The difference between switching power supplies and linear power supplies is mainly the way they work.

Linear power supply power device works in linear state, that is to say, it is used power device is always working, so it leads to its low work efficiency, generally in 50% ~ 60%, but also have to say that he is a good linear power supply. The way the linear power supply works, so that it changes from high voltage to low voltage must have a voltage device, generally a transformer, but also others like KX power supply, and then rectified output DC voltage. In this way, his volume is also large, bulky, inefficient, and calorific. It also has its advantages: small ripple, good adjustment rate, and little external interference. Suitable for analog circuits, various amplifiers, etc.

     Its power device works in the switching state, (one on and one off, one on and one off, the frequency is very fast, the general flat panel switching power supply frequency is 100~200KHz, the module power supply is 300~500KHZ). A little ink, its transformer is a word small. Efficiency 80%~90%. It is said that the best VICOR module in the United States is as high as 99%.The efficiency of the switching power supply is high and the size is small, but compared with the linear power supply, its ripple, voltage and current regulation rate is discounted.