Technical analysis: LED power supply inductive DC-DC boost principle

 Inductor is a component that we use for a long time in transformer design. Its main function is to convert electrical energy into magnetic energy and then store it. It should be noted that although the structure of the inductor is similar to that of a transformer, it has only one winding. This article mainly introduces the principle of the inductive DC-DC booster, and this article is of basic nature, suitable for those who do not understand the characteristics of inductors but are interested in boosters. Some of the principle knowledge in the article can be found on the Internet, so I will not elaborate on it here.

　　To fully understand the principle of inductive boost, we must first know the characteristics of inductance, including electromagnetic conversion and magnetic energy storage. These two points are very important because all the parameters we need are derived from these two characteristics.

　　First, let's look at the following picture:

　　As you all know, the picture above is an electromagnet, where a battery energizes a coil. Some people may wonder, what is there to analyze with such a simple picture? We are going to use this simple picture to analyze what happens when it is powered on and off.

　　The coil (hereinafter referred to as "inductor") has a characteristic - electromagnetic conversion. Electricity can be converted into magnetism, and magnetism can be converted back into electricity. When the power is turned on, the electricity will be converted into magnetism and stored in the inductor in the form of magnetism. When the power is turned off, the magnetism will be converted into electricity and released from the inductor.

　　Now let's look at the picture below to see what happens when the power goes out:

　　As I said before, the magnetic energy in the inductor will be converted back into electricity when the inductor is powered off. However, the question is: how can the magnetism be converted into electricity when the circuit is broken and the current has nowhere to go? It's simple. High voltage will appear at both ends of the inductor! How high can the voltage be? Infinitely high, until it breaks through any medium that blocks the flow of current.

　　Here we understand the second characteristic of inductance - the voltage-boosting characteristic. When the loop is disconnected, the energy in the inductor will be converted back into electricity in the form of infinitely high voltage. How high the voltage can be increased depends only on the breakdown voltage of the dielectric variable.

　　Now let's summarize the above content:

　　The following is a positive voltage generator. If you keep flipping the switch, you can get an infinitely high positive voltage from the input. How high the voltage rises depends on what you connect to the other end of the diode so that the current has a place to go. If nothing is connected, the current has nowhere to go, so the voltage will rise high enough to break down the switch, and the energy will be consumed in the form of heat.

　　Then there is the negative pressure generator. You keep flipping the switch and you can get an infinitely high negative voltage from the input.

　　The above are all theories. Now let's take a look at some actual electronic circuit diagrams to see what the "minimum system" of the positive/negative pressure generator looks like:

　　You can clearly see the evolution, the circuit just replaced the switch with a triode. Don't underestimate these two diagrams, in fact, all switching power supplies are derived from the combination of these two diagrams, so it is very important to master these two diagrams.

　　Finally, let's talk about magnetic saturation. What is magnetic saturation?

　　From the above background, we know that inductors can store energy and preserve it in the form of magnetic fields, but how much can it store? What happens when it is full?

　　1. How much is stored: The "maximum magnetic flux" parameter is used for this purpose. Obviously, the inductor cannot store energy infinitely. The amount of energy it stores is determined by the product of voltage and time. For each inductor, this is a constant. Based on this constant, you can calculate how high a frequency an inductor must operate at to provide N volts and megaamperes of power.

　　2. What happens when the inductor is fully charged? This is the problem of magnetic saturation. After saturation, the inductor loses all the characteristics of an inductor and becomes a pure resistor, dissipating energy in the form of heat.