This article introduces the principle of inductive DC-DC boosters, a fundamental concept suitable for those who are unfamiliar with inductive characteristics but have an interest in boost circuits.
To fully grasp the principle of inductive step-up, it's essential to understand the characteristics of inductance, including electromagnetic conversion and magnetic energy storage.
Let's take a look at the following image:
This image depicts a battery powering an inductor (coil), which has a characteristic called electromagnetic conversion—the ability to transform electricity into magnetism and vice versa. Instantly upon power application, the electricity is converted into magnetism and stored within the inductor. Upon power interruption, the magnetism reverts back to electricity, releasing it from the inductor.
However, a problem arises: after the power outage, the circuit is broken, and there is nowhere for the current to flow. How can magnetism be converted into electricity? It's simple; high voltage will appear at both ends of the inductor. If the inductance coefficient of the inductor is very large, the induced electromotive force will also be very large. In the gap between the large potential difference, a strong electric field will be generated, which could even puncture the air, causing a discharge. If there are people nearby, they may be at risk. If there are flammable materials in the vicinity, there is a risk of fire.
We now understand two characteristics of inductors—the voltage-increasing property. When the circuit is opened, the energy within the inductor is transformed back into electricity in the form of high voltage.
Now, let's summarize the above content.
Below is a positive voltage generator. As you keep toggling the switch, a high positive voltage can be obtained from the nodes shown in the diagram. The voltage can rise to what extent depends on what you connect to the other side of the diode to allow the current to flow. If nothing is connected, the current has nowhere to go, causing the voltage to rise to a point high enough to puncture the switch, dissipating the energy in the form of heat.
Then, it's the vacuum generator. By continuously toggling the switch, you can obtain a high negative voltage at the points shown in the diagram.
Above are all theories, now let's dive into the practical aspect with a look at the DC-DC boost circuit system and see what it actually looks like.
You can clearly see the evolution: replacing the switch in the circuit with a transistor, and using a fixed-frequency square wave to control the transistor's switch can achieve voltage boosting. Don't underestimate these two diagrams; in fact, all switching power supplies are composed and transformed from these two diagrams.
Discuss the issue of magnetic saturation.
We know that inductors can store energy, preserving it in a magnetic field. But how much can they hold, and what happens when they're full?
Flux density, a parameter indicating how much energy an inductor can store, allows you to calculate the frequency at which an inductor must operate to provide a current of n volts per ampere.
What happens when it's full? That's the issue of magnetic saturation. Once saturated, the inductor loses its electromagnetic induction properties and becomes a pure resistor, dissipating energy in the form of heat.
