What's the difference between switching power supply and ordinary power supply?
Ordinary power supply is generally linear power supply. Linear power supply refers to the power supply in which the regulating tube works in a linear state. In switching power supply, it is different. The switching tube (in switching power supply, we generally call the adjusting tube switching tube) works in two states: on-low resistance; Off-the resistance is very high.
Switching power supply is a relatively new type of power supply. It has the advantages of high efficiency, light weight, step-up and step-down, and high output power. However, because the circuit works in the switch state, the noise is relatively large. Let's briefly talk about the working principle of buck switching power supply through the following figure. As shown in the figure, the circuit consists of a switch K (actually a triode or a field effect transistor), a freewheeling diode D, an energy storage inductor L, a 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 electric energy in the inductor L and the capacitor C.. Due to the self-inductance of inductance L, the current increases slowly after the switch is turned on, that is, the output cannot reach the power supply voltage immediately. After a certain period of time, the switch is turned off, and the current in the circuit will remain unchanged, that is, it will continue to flow from left to right, due to the self-inductance of the inductor L (it can be thought that the current in the inductor has inertia). This current flows through the load, returns from the ground, 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 closing and opening time of the switch (namely PWM-pulse width modulation), the output voltage can be controlled. If the on-off time is controlled by detecting the output voltage to keep the output voltage unchanged, the purpose of voltage stabilization is realized.
The common power supply and switching power supply have the same voltage regulating tube, which uses the feedback principle to stabilize the voltage. The difference is that switching power supply uses the switching tube to adjust, and ordinary power supply generally uses the linear amplification region of triode to adjust.
Comparatively speaking, switching power supply has low energy consumption, wide application range for AC voltage and good ripple coefficient of output DC, but its disadvantage is switching pulse interference.
The main working principle of ordinary half-bridge switching power supply is that the switching tubes of the upper bridge and the lower bridge (VMOS when the frequency is high) are turned on in turn. First, the current flows in through the switching tube of the upper bridge, and the storage function of the inductor coil is used to concentrate the electric energy in the coil. Finally, the switching tube of the upper bridge is turned off, and the switching tube of the lower bridge is turned on. The inductor coil and the capacitor continuously supply power to the outside. Then turn off the lower bridge switch tube, and then turn on the upper bridge to let the current in, and so on. Because the two switch tubes have to be turned on and off in turn, it is called switching power supply.
The linear power supply is different. Because there is no switch to intervene, the water supply pipe has been discharging water. If there is too much, it will leak out. This is what we often see. The regulating tubes of some linear power supplies have a large calorific value, and all the inexhaustible electric energy is converted into heat energy. From this point of view, the conversion efficiency of linear power supply is very low, and when the heat is high, the life of components is bound to decline, which will affect the final use effect.
