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 refer to the adjustment tube as the 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.

1. Example: step-down switching power supply

Let‘s briefly talk about the working principle of the step-down switching power supply: the circuit is composed of switches (transistors or field effect transistors in the actual circuit), freewheeling diodes, energy storage inductors, filter capacitors, etc.

When the switch is closed, the power supply supplies power to the load through the switch and the inductor, and stores part of the electrical energy in the inductor and capacitor. Due to the self-inductance of the inductor, after the switch is turned on, the current increases relatively slowly, that is, the output cannot immediately reach the power supply voltage value.

After a certain period of time, the switch is turned off. Due to the self-inductance effect of the inductor (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, passes through the diode, and returns to the left end of the inductor, 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 ripple coefficient of output DC, 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.

2. The main difference: how it works

The power regulating tube of the linear power supply always works in the amplification area, and the current flowing through it is continuous. Due to the large power loss on the adjustment tube, a larger power adjustment tube is required and a large radiator is installed. power supply).

The working mode of the linear power supply requires a step-down device to change from high voltage to low voltage. Generally, it is a transformer, and there are others like KX power supply, and then output DC voltage through rectification. In this way, the volume is large, relatively bulky, low efficiency, and large heat generation; but it also has advantages: small ripple, good adjustment rate, small external interference, suitable for analog circuits/various amplifiers, etc.

The power device of the switching power supply works in the switching state, and the energy is temporarily stored through the inductive coil when the voltage is adjusted, so that its loss is small, the efficiency is high, and the requirement for heat dissipation is low. There are also higher requirements, which should be made of materials with low loss and high magnetic permeability. Its transformer is a small word. The total efficiency is 80% to 98%. The efficiency of the switching power supply is high but the volume is small, but compared with the linear power supply, the voltage and current regulation rate has a certain discount.

The above is the difference between switching power supply and ordinary power supply, I hope to help everyone.