Comparison between switching power supply and Linear Power Supply

Source: Internet
Author: User

The adjustment tube of the linear power supply is working in a magnified state, so the heat is generated and the efficiency is low (about 35%). A large heat sink is required, and a large power frequency transformer is also required, the transformer will be larger when multiple voltage outputs are to be made.

The adjustment tube of the switch power supply is working in saturation and cutoff state, so it has a small calorific value, a high efficiency (more than 75%) and saves a large volume of transformer. However, the DC output from the switch power supply overwrites large ripple.
50mV at 5 V output
Typical), the voltage regulator diode can be improved at the output end. In addition, because the operation of the switch will produce a great deal of peak pulse interference, it also needs to be improved in the circuit. Relatively Linear Power Supply
There is no such defect, and Its ripple can be very small (less than 5mV ).

It is better to use the switching power supply where the power supply efficiency and installation volume are required, and to choose multiple linear power supplies where the electromagnetic interference and power supply purity are required (such as capacitive leakage detection. In addition, when the circuit needs to be isolated
Most of the current use of DC-DC to isolate part of the power supply (DC-DC from its working principle is the switching power supply ). In addition, the high-frequency transformers used in the switching power supply may be difficult to bypass.

The switching power supply and linear power supply are completely different in the internal structure. As the name suggests, the switching power supply has a switch action. It uses the method of changing the duty cycle or frequency conversion to realize different voltages, which is more complicated to achieve, the biggest advantage is the high
The efficiency is generally above 90%. The disadvantage is that the noise of the Wenbo and switch is high, which is suitable for scenarios with low requirements on the Wenbo and noise. The linear power supply has no switching action and is a 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, the biggest drawback is low efficiency. Each of them has its own shortcomings!

I. Principle of linear power supply:

Linear Power supply mainly includes power frequency transformer, output rectifying filter, control circuit, protection circuit, etc.
A linear power supply first transformer the alternating current, and then transformer and filter through the rectification circuit to obtain unstable DC voltage. To achieve high precision DC voltage, the output voltage must be adjusted through voltage feedback, this power technology
Technology is very mature, can achieve high stability, ripple is also very small, and no switching power supply with interference and noise. However, its disadvantage is that it requires a large and bulky transformer, and the size and weight of the filter capacitor are also required.
The voltage feedback circuit is working in a linear state, and the adjustment tube has a certain voltage drop. When the output is large, the power consumption of the adjustment tube is too large, the conversion efficiency is low, and a large heat sink needs to be installed.
This type of power supply is not suitable for computer and other equipment, and will be gradually replaced by the switch power supply.

Ii. Principle of switching power supply:

The switching power supply mainly includes the input power grid filter, the input rectifying filter, the inverter, the output rectifying filter, the control circuit, and the protection circuit. Their functions are as follows:
1. input grid filter: eliminate interference from power grids, such as Motor Startup, electrical switch, and lightning strikes, and prevent high-frequency noise from switching power supplies from spreading to the power grid.

2. Input rectifying 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 switch power supply. It converts DC voltage to High-Frequency AC voltage and isolates the output part from the input grid.

4. output rectifying filter: the high-frequency AC voltage output by the converter is rectified and filtered to obtain the required DC voltage, and the high-frequency noise is also prevented from interfering with the load.

5. Control Circuit: Detect the output DC voltage and compare it with the reference voltage to enlarge it. Modulated 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 will stop the switching power supply to protect the load and power supply itself.
The switching power supply first rectifies the AC power into the DC power. When the DC is converted into the AC power, the required DC voltage is output in the rectification. In this way, the switching power supply saves the power transformers in the linear power supply and the voltage feedback circuit. The inverter circuit in the switch power supply is completely digital adjustment, and can also achieve very high adjustment accuracy.

Main advantages of switching power supply:

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

Main disadvantages of switching power supply:

High-frequency voltage is generated in the inverter circuit, which may affect the peripheral devices. Good shielding and grounding are required
Power-off is to use the circuit to control the switch tube for High-Speed Channel Access and cut-off. The DC power is converted to High-Frequency AC power supply to the transformer for pressure change, thus generating a set or multiple groups of voltage required! Switch to Huawei High Frequency
The reason for alternating current is that the efficiency of High-Frequency AC in Transformer Voltage change circuit is much higher than 50Hz, so the switch transformer can be very small, and it is not very hot at work !! Low cost. If 50Hz is not changed
For high frequency, switching power supply is meaningless !! The switch transformer is no secret. It's just a normal transformer! This is the switch power supply.
The switching power supply is achieved through electronic technology. The main link is to convert the power supply to DC-convert the power supply to the required voltage (mainly to adjust the voltage)-and then convert the power supply to the DC voltage output.
The switch power supply structure has no transformer and heat sink in the middle, so the size is very small. At the same time, the switch power supply is inside the electronic components, high efficiency, low fever. Although it has shortcomings such as electromagnetic interference, the current shielding technology is already in place.
The switch power supply can be divided into two types: Isolation and non-isolation. The isolated type must have a switch transformer, but not the isolated type may not.

To put it simply, the working principle of the switching power supply is:

1. AC power input is rectified and filtered into DC;
2. Control the switch through high-frequency PWM (Pulse Width Modulation) signal, and add the DC to the switch transformer entry;
3. The switch transformer generates high-frequency voltage and is provided to the load by rectifying and filtering;
4. The output part is fed back to the control circuit through a certain circuit to control the PWM duty cycle to achieve stable output.

When the AC power supply is input, it usually goes through the erliu sphere to filter out the interference from the power supply and the power supply to the power grid. When the power supply is the same, the switch frequency is higher, the smaller the volume of the switch transformer,
However, the requirement for the switch tube is higher. The switch transformer can have multiple windings or one winding has multiple headers to obtain the desired output. In general, some protection circuits should be added, such as no-load and short-circuit protection,
Otherwise, the switch power supply may be burned out.
The above is the general working principle of the switching power supply.
In fact, now we have a dedicated chip with a very high degree of integration, which can make the peripheral circuit very simple, or even achieve debugging-free.
For example, the top series switch power supply chip (or module), as long as some resistance components, and a switch transformer, can be made into a basic switch power supply.

Switching Power Supply & linear power supply

the main working principle of the switching power supply is the mos wheel of the upper and lower bridges.
flow conduction, first, the current flows through the mos tube on the bridge, and uses the storage function of the coil to gather power in the online circle. Finally, the mos tube on the bridge is closed and the mos tube on the bridge is opened, the coil and capacitor are continuously supplied to the outside
. Then shut down the downstream MOS tube, and then open the upper bridge to let the current enter, so we will repeat it, because we need to switch the mos tube in turn, so it is called the switching power supply.
the linear power supply is different. Because no switch is involved, the water pipes are always flushed. If there are many power supplies, they will be leaked, this is what we often see is that some Linear Power Supply of MOS Tube Heat is very large, with no
finished power, 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 decrease, affecting the final use effect.
the main difference between a Switched power supply and a linear power supply is the way they work.
the power supply device is working in a linear state. In other words, when used, the power device is always working, which leads to low efficiency, generally between 50% and ~ 60%, it must be said that he is a good linear electrical
source. The linear power supply work in a way that changes from high voltage to low voltage. There must be a pressure device. Generally, it is a transformer, and there are other power supplies like kx, which are then rectified to output the DC voltage. In this way, his volume is very large.
it is heavy, inefficient, and has a large heat. He also has his advantages: small ripple, good adjustment rate, and small external interference. Suitable for use with analog circuits, various types of amplifiers, etc.
switch power supply. The power device is working on or off the switch. (The switching frequency is very fast when the power device is on or off. The general flat-panel Switching Power Supply frequency is between 100 and ~ 200 kHz, module power supply in
300 ~ 500 kHz ). in this way, the loss will be small, and the efficiency will be high. The transformer also needs to be made of materials with high permeability. A little ink, his transformer is a small character. 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 small, but the voltage and current adjustment rate is discounted compared with the linear power supply.

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