What is a 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 a switch (transistor or field effect tube in the actual circuit), a freewheeling diode, an energy storage inductor, and a filter capacitor.
When the switch is closed, the power supply supplies power to the load through the switch and the inductor, and stores part of the electric energy in the inductor and capacitor. Due to the self-inductance of the inductance, after the switch is turned on, the current increases slowly, that is, the output cannot reach the power supply voltage value immediately.
After a certain period of time, the switch is turned off, and due to the self-inductance of the inductor (it can be compared visually that the current in the inductor has an inertial effect), the current in the circuit will remain unchanged, that is, 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 when the switch closes and opens (ie PWM - Pulse Width Modulation), the output voltage can be controlled. If the on and off time is controlled by detecting the output voltage to keep the output voltage constant, the purpose of voltage regulation is achieved.
The main working principle of the ordinary half-bridge switching power supply is that the switching tubes of the upper bridge and the lower bridge (when the frequency is high, the switching tube is VMOS) are turned on in turn. First, the current flows in through the switching tube of the upper bridge. In the coil, the switch tube of the upper bridge is finally turned off, and the switch tube of the lower bridge is turned on, and the inductance coil and the capacitor continue to supply power to the outside. Then turn off the switch tube of the lower bridge, and then open the upper bridge to let the current enter, and repeat like this, because the two switch tubes need to be turned on and off in turn, so it is called a switching power supply.
