Linear power, switching power difference

The adjustment tube of linear power supply works in the state of amplification, so it generates large amount of heat and has low efficiency (about 35%). It needs to add large heat sink, and also needs the power frequency transformer which is also large volume. When making multiple voltage output groups, the transformer will be larger. 

The regulator of the switching power supply works in the saturated and off state, thus generating less heat, being efficient (over 75%) and eliminating the need for large transformers.However, a large ripple (50mV at 5V output typical) will be superimposed on the dc output of the switching power supply. It can be improved by connecting the voltage regulator diode at the output end. In addition, since the switching tube will produce a large spike pulse interference, it is also necessary to connect magnetic beads in the circuit to improve it.Relatively speaking, linear power supply does not have the above defects, and its ripple can be done very small (under 5mV). 

Switching power supply is preferred where power supply efficiency and installation volume are required, and linear power supply is preferred where electromagnetic interference and power supply purity are required (such as capacitor leakage detection).In addition, when the circuit needs to be isolated, now most use dc-dc 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 difficult to wrap up

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 switching action and 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, low noise and low efficiency.They each have shortcomings in the application of complementary coexistence! 

Principle of linear power supply:

Linear power supply mainly includes power frequency transformer, output rectifier filter, control circuit, protection circuit and so on.Linear power supply is alternating current through the transformer transformer, first through the rectifier circuit dc voltage of the rectifier filter is not stable, to achieve high-precision dc voltage, must pass a voltage feedback to adjust the output voltage, the power supply technology is mature, can achieve a high degree of stability, ripple is small, and there is no switch power supply with the interference and noise.But its drawback is that need to be large and heavy transformer, the required the volume and weight of the filter capacitor is also quite big, and the voltage feedback circuit is working in linear state, adjust the tube voltage drop to a certain extent, on the work in a larger output current, which adjust the tube power consumption is too large, conversion efficiency is low, and install a lot of heat sink.This kind of power supply is not suitable for the needs of computers and other equipment, and will be gradually replaced by switching power supply. 

Ii. Principle of switching power supply

Switch power supply mainly includes input network filter, input rectifier filter, inverter, output rectifier filter, control circuit, protection circuit.Their functions are:

1, input network filter: eliminate the interference from the grid, such as the start of electric motors, electrical switches, lightning strikes, etc., and prevent the high-frequency noise generated by the switching power supply from spreading to the 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 the key part of switching power supply.It converts dc voltage into high frequency ac voltage and isolates the output part from the input grid. 

4. Output rectifier filter: the high-frequency ac voltage output by the converter is rectified and filtered to get the required dc voltage, while preventing the interference of high-frequency noise 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 to control the converter to keep the output voltage stable. 

6, protection circuit: when the switch power supply occurs overvoltage, overcurrent short circuit, the protection circuit makes the switch power supply stop working to protect the load and the power supply itself. 

Switching power supply is the first ac rectifier into direct current, in the dc inverter into ac, in the rectifier output into 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 digital adjustment, which can also achieve very high adjustment accuracy. 

Main advantages of switching power supply:

Small volume, 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, modularization. 

Main disadvantages of switching power supply:

Due to the high frequency voltage generated in the inverter circuit, there is some interference to the surrounding equipment.Good shielding and grounding is required

Switching power supply is to use the circuit to control the switch tube for high-speed passage and cut-off.The conversion of direct current to high frequency alternating current is provided to the transformer for voltage conversion, thus generating the required group or 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 switch transformer can do very small, and the work is not very hot!!The cost is very low.If you don't convert 50Hz to high frequency then there is no point in switching power!!Switching transformers are no mystery.Just an ordinary transformer!This is the switching power supply. 

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

Switch power supply structure because there is no transformer and radiator fin in the middle, so the volume is very small.At the same time, the internal switch power supply is electronic components, high efficiency, small heating.Although, has electromagnetic interference and other shortcomings, but the current shielding technology has been very in place. 

Switch power supply can be divided into isolation and non-isolation two kinds, isolation type must have switch transformer, and not necessarily have isolation. 

Simply put, the switching power supply works as follows:

1. Ac power input is filtered into dc through rectification; 

2. The switch tube is controlled by high-frequency PWM(pulse width modulation) signal, and the dc is added to the primary switch transformer; 

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

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

When ac power is input, it usually goes through something like an alternating current coil to filter out the interference on the power grid, and at the same time to filter out the interference of the power supply on the power grid.At the same power, 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 may have multiple windings or multiple taps in one winding to obtain the desired output;Generally, some protection circuits should be added, such as no-load, short circuit protection, otherwise it may burn down the switch power supply. 

This is the general principle of switching power supply. 

In fact, now there are special chips with very high integration, which can make the peripheral circuit very simple, even debugging free. 

For example, the TOP series switching power supply chip (or module) can be made into a basic switching power supply as long as it is combined with some resistive and capacitive elements and a switching transformer. 

Switching power & linear power

The main working principle of switching power supply is to conduct the Mos tube of the upper bridge and the lower bridge in turn. Firstly, the current flows in through the Mos tube of the upper bridge. By using the storage function of the coil, electric energy is gathered in the coil.Then turn off the lower bridge Mos tube, and then open the upper bridge to let the current enter, and repeat in this way. Since the Mos tube needs to be switched on and off in turn, it is called the switching power supply. 

However, the linear power supply is different. Because there is no switch to intervene, the upper water pipe keeps discharging water. If there is too much, it will leak out.From this point of view, the conversion efficiency of linear power supply is very low, and when the heat is high, the service life of the components is bound to decline, affecting the final use effect. 

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

Linear power supply power devices work in a linear state, that is to say, they work all the time when they are used, so their working efficiency is low, generally at 50%~60%, and they are very good linear power supply.Linear power supply work mode, make him from high voltage to low voltage must have voltage device, general are transformers, there are other like KX power supply, and then through rectification output dc voltage.As a result, it was bulky, cumbersome, inefficient and calorific.He also has his advantages: small ripple, good adjustment rate, low external interference.Suitable for analog circuits, amplifiers, etc. 

Switch power supply.His power devices work in the switching state (one on, one off, one on, one off, very fast frequency, the general plate switching power frequency in 100~200KHz, module power in 300 ~ 500KHZ).In this way, his loss is small, the efficiency is high, the transformer also has requirements, to use high permeability material to do.It's a little inky. His transformer is a little word.80% to 90% efficiency.It is said that the best VICOR module in America is 99%.Switching power supply is efficient and small in size, but compared with linear power supply, voltage and current adjustment rate has a discount