Inductor Secret: Working Principle of Minimal Inductance

Mar 23,2023

With the development of semiconductor materials, the third generation of gallium nitride and silicon carbide semiconductors have gradually entered people's vision, continuously reducing the size of chargers. A multi port charger that supports simultaneous charging of multiple devices has greatly facilitated our lives. Low-power mobile power sources are also gradually exiting the market, and more and more high-power fast charging charging batteries are entering the market. The size is not significantly different from ordinary charging batteries, but they support high-power input and output.
The purpose of power inductors is often to build LC filter circuits at the output of switching power supplies, where L is the power inductor (C is the output capacitance). Understanding this level is not enough. In order to optimize the design of inductors, even in many situations, the heating and height issues focus on inductors. We must understand what components make up the heating of inductors. As electronic products become smaller and thinner, it will eventually be necessary to clarify this issue. In order to solve the heating problem, it is necessary to have a deeper understanding of the nature of the behavior of inductors during operation.
In many switching power supply topologies, the application principle is the same. Let's take a buck topology as an example, as shown in Figure 1. One side of the inductor is connected to the input or GND at the switching point of the power switch, and the other side is connected to the output voltage. In the circuit, Q1 power transistors and CR1 power freewheeling diodes switch back and forth at high speed for operation. With the improvement of semiconductor technology, more and more freewheeling diodes in Buck circuits have been replaced by power switches, and have been widely used in many fields.
Note that when both the upper and lower tubes (also known as High Side and Low Side) are power switches, the two power tubes are not allowed to be turned on simultaneously (if they are turned on at the same time, the loop impedance input to GND is the lowest, causing a direct short circuit, and causing the circuit to fail). Therefore, the upper and lower tubes must be turned on and off at an appropriate time to allow the two tubes to work alternately, which is called "dead time". That is, when Q1 is turned on, Q2 must be turned off, and when Q2 is turned on, Q1 must be turned off, and synchronization control must be performed very accurately. Therefore, both the top and bottom are power switching circuits of power switches, also known as synchronous rectifier power conversion.