Ordinary power supply is generally linear power supply, linear power supply refers to the power supply in which the adjustment tube works in a linear state. In the switching power supply, it is different. The switching tube (in the switching power supply, we generally call the adjusting tube a switching tube) works in two states: on and off: on - the resistance is very small; off - the resistance is very high big.
Switching power supply is a relatively new type of power supply. It has the advantages of high efficiency, light weight, step-up, step-down, and large output power. However, since the circuit works in the switching state, the noise is relatively large. Through the following figure, let's briefly talk about the working principle of the step-down switching power supply. As shown in the figure, the circuit is composed of switch K (transistor or field effect transistor in the actual circuit), freewheeling diode D, energy storage inductor L, filter capacitor C, etc. When the switch is closed, the power supply supplies power to the load through the switch K and the inductor L, and stores part of the electrical energy in the inductor L and the capacitor C. Due to the self-inductance of the inductor L, after the switch is turned on, the current increases relatively slowly, that is, the output cannot reach the power supply voltage value immediately. After a certain period of time, the switch is turned off. Due to the self-inductance effect of the inductor L (it can be visualized that the current in the inductor has an inertial effect), the current in the circuit will remain unchanged, that is, it will continue to flow from left to right. This current flows through the load, returns from the ground wire, flows to the anode of the freewheeling diode D, passes through the diode D, and returns to the left end of the inductor L, thus forming a loop. By controlling the time the switch closes and opens (ie PWM - Pulse Width Modulation), the output voltage can be controlled. If the ON and OFF times are controlled by detecting the output voltage to keep the output voltage unchanged, the purpose of voltage regulation is achieved.
The common power supply and the switching power supply have the same voltage regulation tube, which uses the feedback principle to regulate the voltage.
In comparison, switching power supply has low energy consumption, wider application range for AC voltage, and better output DC ripple coefficient, but the disadvantage is switching pulse interference.
The main working principle of an ordinary half-bridge switching power supply is that the switches of the upper bridge and the lower bridge (the switch is VMOS when the frequency is high) are turned on in turn. First, the current flows in through the upper bridge switch, and the storage function of the inductance coil is used to gather the electric energy. In the coil, the upper bridge switch tube is finally turned off, the lower bridge switch tube is turned on, and the inductor coil and capacitor continue to supply power to the outside. Then turn off the lower bridge switch, then turn on the upper bridge to let the current in, and repeat this process, because the two switches are turned on and off, so it is called a switching power supply.
The linear power supply is different. Since there is no switch intervention, the upper water pipe is always releasing water. If there is too much, it will leak out. This is what we often see in the adjustment tube of some linear power supplies. 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.
