Some functions of switching power supply
Switching power supply mainly includes input grid filter, input rectification filter, inverter, output rectification filter, control circuit and protection circuit. Their functions are:
1. Input grid filter: Eliminate interference from the 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 grid.
2. Input rectification filter: rectify and filter the input voltage of the grid to provide DC voltage for the converter.
3. Inverter: It is a key part of switching power supply. It transforms the DC voltage into a high-frequency AC voltage and plays a role in isolating the output part from the input grid.
4. Output rectification filter: rectify and filter the high-frequency AC voltage output by the converter to obtain the required DC voltage, and at the same time prevent high-frequency noise from interfering with the load.
5. Control circuit: detect the output DC voltage, compare it with the reference voltage, and amplify it. The pulse width of the oscillator is modulated to control the converter to keep the output voltage stable.
6. Protection circuit: When the switching power supply has an 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 the alternating current into direct current, then inverts the direct current into alternating current, and then rectifies and outputs the required direct current voltage. In this way, the switching power supply saves the transformer in the lower 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.
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 tube of the upper bridge, and the electric energy is accumulated in the coil by using the storage function of the coil. Finally, the Mos tube of the upper bridge is turned off, and the lower bridge is turned on. The Mos tube, coil and capacitor of the bridge continuously supply power to the outside. Then turn off the lower bridge Mos tube, and then open the upper bridge to let the current enter, and repeat like this, because the Mos tube needs to be switched on and off in turn, so it is called a switching power supply.
The linear power supply is different. Since there is no switch involved, the upper water pipe is always discharging water. If there is too much water, it will leak out. This is what we often see in some linear power supplies. The Mos tube generates a lot of heat. The endless electrical 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 components is bound to decrease, affecting the final use effect.
